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AN INTRODUCTION TO PHYSIOLOGY 



AN INTRODUCTION 



TO 



PHYSIOLOGY 



BY 



WILLIAM TOWNSEND PORTER, M.D. 

ASSOCIATE PROFESSOR OP PHYSIOLOGY IN THE 
HARVARD MEDICAL SCHOOL 



THE UNIVERSITY PRESS 

(JTambrtop, $flass* 
1906 



LIBRARY of CONGRESS 
Two Copies Received 

JAi* 31 1906 

Copy riff ht Entry 

9^.2^- '<?°<> 

«LASS O^ XXc. No. 

COPY B. 



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Copyright, 1906, 
By W. T. Porter. 



PREFACE TO THE SECOND EDITION 

Concentration, sequence, and election are 
fruitful principles in the higher education. 

In 1898 the Committee on Medical Education, 
appointed by the Harvard Faculty of Medicine, 
reported in favor of the " concentration " system 
urged in the committee by the author in com- 
mon with Professor W. T. Councilman. By this 
method, the first half-year in the Medical School 
is devoted to anatomy and histology, the second 
half-year to physiology and biological chemistry, 
the third half-year to pathology and bacteriology, 
and the fourth, fifth, and sixth half-years to 
practical medicine and surgery. Work under 
the new system began in the collegiate year of 
1899-1900. In 1904, largely through the influ- 
ence of Professor Bowditch, the seventh and 
eighth half-years were made elective, each stu- 
dent choosing for himself the studies best suited 
to his needs. 

Concentration provides that the student shall 
not serve two masters, but shall study at one 



VI PREFACE TO THE SECOND EDITION 

time only one principal subject, such as physi- 
ology or pathology, disciplines that do not yield 
readily to a divided mind. Sequence provides 
that a foundation shall be laid before the super- 
structure is attempted. Students now have an 
acquaintance with anatomy before they begin 
the study of physiology. Election somewhat 
tardily intrusts to university men rarely less 
than twenty-five years ' of age a voice in the 
decision of their nearest affairs. The application 
of these principles to medical teaching has un- 
doubtedly resulted in large savings of time and 
energy. 

The economy of force secured by concentra- 
tion and sequence has been highly valuable, 
though not indispensable, in the new teaching of 
physiology introduced by the author in Feb- 
ruary, 1900. The traditional teaching of physi- 
ology consists of lectures illustrated by occasional 
demonstrations and, in some instances, by experi- 
ments performed by the students themselves. 
The new method is fundamentally opposite. It 
consists of experiments and observations by the 
student himself. The didactic instruction, com- 
prising lectures, written tests, recitations, confer- 
ences, and the writing and discussing of theses, 
follows the student's experiments and considers 
them in relation to the work of other observers. 



PKEFACE TO THE SECOND EDITION Vll 

In the old method, the stress is upon the di- 
dactic teaching. In the new there is no less 
didactic teaching, but the stress is upon observa- 
tion. The old method insensibly teaches men to 
rest upon authority, but the new directs them 
to nature. 

The new method requires : 

1. Printed accounts of the fundamental experi- 
ments and observations in physiology, taken from 
the original sources, and arranged in the most 
instructive sequence. The reference to the origi- 
nal source should be given in each case. 

2. Accessory data grouped about the funda- 
mental experiments. The accessory data should 
also be taken as directly as possible from the 
original sources, and the reference given in each 
case. 

3. Apparatus of precision designed with the 
utmost simplicity upon lines that permit its 
manufacture in large quantities at small cost. 

It is obvious that these conditions cannot be 
met without prolonged labor. Meanwhile, the 
annual classes in physiology must be taught. 
The present volume is a collection of fundamen- 
tal and accessory experiments in several fields 
printed in an abbreviated form for the temporary 
use of Harvard Medical students and other inter- 
ested persons. This collection is being completed 



Vlll PREFACE TO THE SECOND EDITION 

and improved as rapidly as possible, and the data 
for the remaining fields are being brought to- 
gether. In its final form this material will con- 
stitute " A Laboratory Text-book of Physiology." 

The Harvard Medical School, 
January, 1906. 



CONTENTS 

PAKT I 

THE GENERAL PROPERTIES OF 
LIVING TISSUES 

I 

Page 
Introduction ..... 3 

Nerve-muscle preparation — Preliminary considerations 
regarding energy, stimulation) and irritability. 

II 

Methods of Electrical Stimulation 

Introduction . 12 

Kinetic theory — Osmotic pressure — Plasmolysis. Isotony 
— Estimation of osmotic pressure in the blood serum — 
Surface tension — Electrolysis — Electrolytic solution 
pressure. 

The Electrometer, the Kheochord, and the Cell 34 
Surface tension altered by electrical energy — Electrom- 
meter — Kheochord — Long rheochord — Square rheo- 
chord — Simple key — Short-circuiting key — Polariza- 
tion — Pole-changer — Polarization current — Dry cell. 

Induction Currents 53 

Inductorium — Magnetic induction — Magnetic field. 
Lines of force — To produce electric induction, lines 
of magnetic force must be cut by circuit — Electro- 
magnetic induction — On the construction of the induc- 
torium — Empirical graduation of inductorium — Plat- 
inum electrodes — Flat-jawed clamp — Pound-jawed 



X CONTENTS 

Page 
clamp — Double clamp — Make and break induction 
currents as stimuli — Extra currents at opening and 
closing of primary current — Tetanizing currents — In- 
duction in nerves — Exclusion of make or break current. 
Unipolar Induction 71 



m 

The Graphic Method 

The Graphic Method 77 

Kymograph — Long paper kymograph — Light muscle 
lever — Writing lever — Tuning fork. 



IV 

The Electrical Stimulation of Muscle axd Nbkvs 

The Galvanic Current 93 

Non-polarizable electrodes — Moist chaml D - : ac- 

tion of the brain by pithing — Paralysis of voluntary 
motion by curare — Opening and closing contraction 
— Changes in intensity of stimulus. 

Polar Stimulation of Muscle 101 

Ureter — Gaskell Clamp — Intestine — Electro-magnetic 
signal — Tonic contraction — Physiological anode and 
cathode — Polar stimulation in heart. 

Polar Stimulation of Xerve 113 

Law of contraction — Changes in irritability — Changes in 
conductivity. 

Stimulation of Human Nerves 127 

Stinmlation of motor points — Polar stimulation of human 
nerves — Brass electrodes — Eeaction of degeneration. 

Galtanotropism 137 

Paramecium. 

Influence of Duration of Stimulus 138 

Tonic contraction — Ehythmic contraction — Continuous 
galvanic stimulation of nerve may cause periodic dis- 



CONTENTS XI 

Page 
charge of nerve impulses — Polarization current — Polar 
fatigue — Opening and closing tetanus — Polar excitation 
in injured muscle. 
Polar Inhibition by the Galvanic Current . . . 153 

Heart — Polar inhibition in veratrinized muscle. 
Stimulation affected by the Form of the Muscle 156 
Effect of the Angle at which the Current Lines 

cut the Muscle Fibres 157 

The Induced Current 158 

V 

Chemical and Mechanical Stimulation 

Chemical Stimulation 163 

Effect of distilled water — Strong saline solutions — Dry- 
ing — " Normal saline " — Importance of calcium — 
Constant chemical stimulation may cause periodic 
contraction. 
Mechanical Stimulation . . . . „ 166 

Idio-muscular contraction.! 



VI 

Irritability and Conductivity 

Irritability and Conductivity 168 

Independent irritability of muscle — Irritability and con- 
ductivity are separate properties of nerve — Minimal and 
maximal stimuli; threshold value — Summation of in- 
adequate single stimuli — Relative excitability of flexor 
and extensor nerve fibres ; Ritter-Rollett phenomenon — 
Specific irritability of nerve greater than that of muscle — 
Irritability at different points of same nerve — Excitation 
wave remains in muscle or nerve fibre in which it starts 
— Same nerve fibre may conduct impulses both centrip- 
etally and centrifugally — Speed of nerve impulse. 



Xll CONTENTS 



PAET II 

THE INCOME OF ENERGY 



Fermentation 

Page 

Hydrolysis of Starch by Diastase 189 

Conversion of starch to sugar by germinating barley — Con- 
version of starch to sugar by salivary diastase (ptyalin) — 
Extraction of diastase from germinating barley — Specific 
action of ferments. 

Proteid Digestion by Pepsin 192 

Gastric digestion of cooked beef and bread — Artificial 
gastric juice — Digestion with artificial gastric juice — 
Extraction of pepsin — Change of proteid to peptone by 
pepsin. 

Splitting of Casein by Rennin 195 

Kennim extract — Separation of rennin — Precipitation of 
casein — Experiments of Arthus and Pages. 

Precipitation of Fibrin by Fibrin Ferment . . . 199 
Buchanan's experiment — Extraction of fibrin ferment — 
Extraction of fibrinogen — Precipitation of fibrinogen by 
fibrin ferment. 

Ammoniacal Fermentation of Urea by Urease . . 201 
Extraction of urease. 

Splitting and Synthesis of Fats 205 

Chemistry of fats and soaps — Splitting of fats by the pan- 
creatic juice — Preparation of neutral fat — The emulsion 
test for fatty acid — Extraction of lipase — Hydrolysis 
of ethyl butyrate by lipase — Synthesis of neutral fat 
by lipase. 



CONTENTS Xlll 

Page 

Immunity 218 

Ehrlich's ricin experiments — Ricin antitoxine — Theory 
of immunity. 
Haemolytic and Bacteriolytic Ferments .... 227 
Bordet's experiments. 

Oxidizing Ferments 230 

Schonbein's experiment — Further oxidations by animal 
tissues — Oxidation by nucleo-proteid — Oxidation about 
the nucleus — Glycolysis in blood — Oxidation not de- 
pendent on living cells of blood — Relation of glycolysis 
to the pancreas and the lymph — Glycolytic ferment of 
pancreas. 

Alcoholic Fermentation 238 

The yeast plant — Chemical relations of carbohydrates. 

Activating Ferments 243 

Enterokinase — Conversion of trypsinogen to trypsin by 
enterokinase. 

Absorption of Proteids 245 

Diffusion of proteids through dead membrane — Diffusion 
through living intestinal wall — Absorption velocity com- 
pared with diffusion velocity — Assimilable proteids — 
Non-assimilable proteids — Alimentary albuminuria — 
Albumose and peptone not ordinarily present in the 
blood or urine — Albumose and peptone changed in their 
passage through the intestinal wall. 

Absorption of Fats, Fat Acids, and Soaps . . . 259 
Absorption of fat — Absorption of fat acids — Absorption 
of fat acid as a soap. 

Lymph 262 

Permeability of vessel wall in inflammation. 



II 

Blood 

Specific Gravity 264 

Drawing the blood — Determination of specific gravity. 
Counting the Corpuscles 266 

Counting the red corpuscles — Counting the white cor- 



XIV CONTENTS 

Page 
Estimation of Haemoglobin 269 

Oxygen capacity of the blood ; the colorimetric determina- 
tion of haemoglobin. 

Haemorrhage and Kegeneration ....... 273 

Physical Aspects of Coagulation 273 

Physical action of salts in the coagulation of colloidal 
mixtures — Physical changes in coagulation. 

Secretion 276 

Speed of absorption and secretion. 

Ill 
Respiration 

Chemistry of Respiration 277 

Estimation of oxygen, carbon dioxide, and water. 

Metabolism 278 

Effect of muscular exercise on the oxygen, carbon dioxide, 
and water of the respired air — Individual level of pro- 
teid metabolism — Nitrogenous equilibrium — Effect of 
muscular exercise on proteid metabolism. 



PAET III 

THE OUTGO OF ENERGY 

I 
Animal Heat 

Animal Heat 285 

Regional temperature — Effect of hot and cold drinks on 
the temperature of the mouth — Hourly variation — Re- 
action of cold and warm blooded animals to changes in 
the external temperature — Chemical action the source 
of animal heat. 



CONTENTS XV 



II 



The Electromotive Phenomena of Muscle and 
Nerve 

Page 

The Demarcation Current of Muscle 287 

Demarcation current of muscle — Stimulation by demarca- 
tion current — Interference between demarcation current 
and stimulating current ; polar refusal. 

Demarcation Current of Nerve 295 

Nerve may be stimulated by its own demarcation current. 

Hypotheses regarding the Causation of the De- 
marcation Current 297 

Action Current of Muscle 302 

Rbeoscopic frog — Action current in tetanus; stroboscopic 
method — Action current of human muscle — Action 
current of heart. 

Action Current of Nerve 315 

Negative variation — Positive variation — Positive after 
current — Contraction secured with a weaker stimulus 
than negative variation — Current of action in optic 
nerve — Errors from unipolar stimulation. 

Secretion Current 320 

Secretion current from mucous membrane — Negative vari- 
ation of secretion current. 

Electrotonic Currents 323 

Negative variation of electrotonic currents ; positive vari- 
ation (polarization increment) of polarizing current 
— Electrotonic current as stimulus. 

Electric Fish 329 



XVI CONTENTS 

III 

The Change in Form 

Page 

Volume of Contracting Muscle 331 

The Single Contraction or Twitch 332 

Muscle curve — Duration of the several periods — Exci- 
tation wave — Contraction wave — Relation of strength 
of stimulus to form of contraction wave — Influence of 
load on height of contraction — Influence of temperature 
on form of contraction — Muscle warmer — Influence of 
veratrine on form of contraction. 

Tetanus 346 

Superposition of two contractions — Superposition in teta- 
nus — Relation of shortening in a single contraction to 
shortening in tetanus. 

The Isometric Method 349 

Graduation of isometric spring — Heavy muscle lever — 
Isometric contraction. 

Contraction of Human Muscle 353 

Simple contraction or twitch — Ergograph — Isometric 
contraction — Artificial tetanus — Natural tetanus. 

Smooth Muscle 356 

Spontaneous contractions — Simple contraction — Tetanus. 

The Work Done 358 

Influence of load on work done — Absolute force of mus- 
cle — Total work done ; the work adder — Total work 
done estimated by muscle curve — Time relations of 
developing energy. 

Elasticity and Extensibility 363 

Elasticity and extensibility of a metal spring — Of a rubber 
band — Of skeletal muscle — Extensibility increased in 
tetanus. 

Fatigue . 366 

Skeletal muscle of frog — Human skeletal muscle. 



CONTENTS XV11 

IV 

The Central Nervous System 

Page 

Simple Reflex Actions 370 

The spinal cord a seat of simple reflexes — Influence of 
afferent impulses on reflex action — Threshold value 
lower in end organ than in nerve-trunk — Summation 
of afferent impulses — Segmental arrangement of reflex 
apparatus — Reflexes in man. 

Tendon Reflexes . 375 

Knee jerk — Ankle jerk — Gower's experiment. 

Effect of Strychnine on Reflex Action .... 377 

Complex Co-ordinated Reflexes 377 

Removal of cerebral hemispheres — Posture, etc. — Bal- 
ancing experiment — Retinal reflex — Croak reflex. 

Apparent Purpose in Reflex Action 381 

Reflex and Reaction Time 382 

Reflex time — Reaction time — Reaction time with choice. 

Inhibition of Reflexes 384 

Through peripheral afferent nerves — Through central 
afferent paths; the optic lobes. 

The Roots of Spinal Nerves 386 

Ludwig's demonstration — Localization of movements at 
different levels of the spinal cord. 

Distribution of Sensory Spinal Nerves .... 388 

Muscular Tonus 389 

Brondgeest's experiment. 

V 

The Skin 

Sensations of Temperature 390 

Hot and cold spots — Outline — Mechanical stimulation 
— Chemical stimulation — Electrical stimulation — Tem- 
perature after-sensation — Balance between loss and gain 



XViil CONTENTS 

Page 
of heat — Fatigue — Eelation of stimulated area to sen 
sation — Perception of difference — Relatively insensitive 
regions. 

Sensations of Pressure 393 

Pressure spots — Threshold value — Touch discrimina- 
tion — Weber's law — After-sensation of pressure — 
Temperature and pressure — Touch illusion ; Aristotle's 
experiment. 

' VI 
General Sensations 

Tickle 398 

Irradiation — After image — Topography — Summation — 
Fatigue. 

Pain .399 

Threshold value — Latent period — Summation — Topog- 
raphy — Individual variation — Temperature stimuli. 

Motor Sensations 400 

Judgment of weight — Sensation of effort — Sensation of 
motion. 

VII 

Taste 

Taste 401 

Threshold value — Topography — Relation of taste to area 
stimulated — Electrical stimulation. 



VIII 

Introduction to Physiological Optics 

Reflection from. Plane Mirrors ....... 403 

Angles of incidence aud reflection. 

Reflection from Concave Mirrors 405 

Principal focus — Conjugate foci — Virtual image — Con- 
struction of image from concave mirrors. 



CONTENTS XIX 

Page 
Reflection from Convex Mirrors 410 

Refraction 410 

Refraction by Prisms 413 

Construction of the path of a ray passing through a prism. 

Refraction by Convex Lenses 416 

Principal focus — Estimation of principal focal distance — 
Conjugate foci — Virtual image — Construction of image 
obtained with convex lens. 

Refraction by Concave Lenses . . 422 

Refraction by Segments of Cylinders 422 

Refraction through Combined Convex and Cylin- 
drical Lenses 424 

Aberration 426 

Spherical aberration by reflection — Spherical aberration 
by refraction — Dispersion circles — Myopia — Hyper- 
metropia — Chromatic aberration — Aberration avoided 
by a diaphragm. 

Numbering of Prisms and Lenses 435 

Numbering of prisms — Numbering of lenses. 

IX 

Kefraction in the Eye 

Refraction in the Eye 437 

The eye as a camera obscura. 
The Schematic Eye 438 

Cardinal Points of the Cornea (System A) . . . 440 
Construction drawing of System A — Principal focal dis- 
tances — Construction of image — Calculation of position 
to conjugate foci. 

Cardinal Points of the Crystalline Lens (System B) 445 
Construction drawing of System B — Optical centre — Nodal 
points — Principal surfaces — The point s — Principal 
points — Principal focal distances. 

Cardinal Points of the Eye (System C) . . . . 451 
Principal surfaces — Nodal points — Principal foci. 



XX CONTENTS 

Page 
Calculation of the Situation and Size of Dioptric 

Images 456 

Reduced Eye 458 

Relations of the Visual Axis 463 

Visual angle — Apparent size — Size of retinal image — 
Acuteness of vision — Smallest perceptible image — 
Measurement of visual acuteness. 

Accommodation 469 

Schemer's experiment — Dispersion circles — Diameter 
of circles of dispersion — Accommodation line. 

Mechanism of Accommodation 473 

Narrowing of pupil — Relation of iris to lens — Changes 
in the lens. 

Measurement of Accommodation ....... 479 

Far point — Determination of far point — Near point — 
Determination of near point — Range of accommodation. 

Ophthalmoscopy 484 

Reflection from retina — Influence of angle between light 
and visual axis — Influence of size of pupil — Influence 
of nearness to pupil — Ophthalmoscope. 

Direct Method 490 

Emmetropia — Ametropia ; qualitative determination — 
Measurement of myopia — Measurement of hypermetro- 
pia — Measurement of astigmatism. 
Indirect Method 496 



X x 

Vision 

Vision 499 

Mapping the blind spot — Yellow spot — Field of vision. 
Color Blindness 501 



Method of examination and diagnosis. 



CONTENTS XXI 

XI 

Mechanics of Respiration 

Page 

Mechanics of Respiration 505 

Artificial scheme — Inspiration — Expiration — Normal 
respiration — Forced respiration — Obstructed air pas- 
sages — Asphyxia — Coughing ; sneezing — Hiccough — 
Perforation of the pleura. 

XII 

The Circulation of the Blood 

The Mechanics of the Circulation 508 

Circulation scheme. 

The Conversion of the Intermittent into a Con- 
tinuous Flow 515 

The Relation between Rate of Flow and Width 

of Bed 519 

The Blood-Pressure 521 

Relation of peripheral resistance to blood-pressure — 
Curve of arterial pressure in the frog — Effect on blood- 
pressure of increasing the peripheral resistance in the 
frog — Changes in the stroke of the pump; inhibition 
of the ventricle — Effect of inhibition of the heart on 
the blood-pressure in the frog. 

The Heart as a Pump 525 

Opening and closing of the valves — Period of outflow 
from the ventricle — Sphygmograph tambour — Visible 
change in form — Graphic record of ventricular contrac- 
tion. 
The Heart Muscle 5S0 

All contractions maximal — Staircase contractions — Iso- 
lated apex ; Bernstein's experiment — Rhythmic con- 
tractility of heart muscle — Constant stimulus may cause 
periodic contraction — Inactive heart muscle still irri- 
table — Refractory period; extra-contraction; compen- 
satory pause — Transmission of the contraction wave 
in the ventricle ; Engelmann's incisions — Transmission 



xxii CONTENTS 



of the cardiac excitation from auricle to ventricle; 
Gaskell's block — Tonus — Influence of "load" on ven- 
tricular contraction — Influence of temperature on fre- 
quency of contraction — Action of inorganic salts on 
heart muscle. 
The Heart Sounds 541 

The Pressure-Pulse 543 

Frequency — Hardness — Form — Volume — Pressure- 
pulse in the artificial scheme — Human pressure-pidse 
curve — Low tension pressure-pulse — Pressure-pulse 
in aortic regurgitation — Stenosis of the aortic valve 
— Incompetence of the mitral valve. 

The Volume Pulse 552 

XIII 

The Innervation of the Heart and Blood-Vessels 

The Innervation of the Heart and Blood- Vessels 554 

The Augmentor Nerves of the Heart 555 

Preparation of the sympathetic — Action of sympathetic 
on heart. 

The Inhibitory Nerves of the Heart 558 

Preparation of the vagus nerve — Stimulation of cardiac 
inhibitory fibres in vagus trunk — Effect of vagus 
stimulation on the auriculo-ventricular contraction in- 
terval — Irritability of the inhibited heart — Intracar- 
diac inhibitory mechanism — Inhibition by Stannius 
ligature — Action of nicotine — Atropine — Muscarine 
— Antagonistic action of muscarine and atropine. 

The Centres of the Heart Nerves 564 

Inhibitory centre — Augmentor centre — Reflex inhibition 
of the heart ; Goltz's experiment — Reflex augmentation. 

The Innervation of the Blood-Vessels .... 568 

Bulbar centre — Vasomotor functions of the spinal cord — 
Effect of destruction of the spinal cord on the distri- 
bution of the blood — Vasomotor fibres leave the cord 
in the anterior roots of spinal nerves — Vasoconstrictor 
fibres in the sciatic nerve — Vasodilator nerves — Reflex 
vasomotor actions. 



ILLUSTRATIONS 

Diagrams which merely illustrate the grouping of apparatus for a par- 
ticular experiment are omitted from this list. 

Fig. Page 

1. Muscles of left hind limb of frog, dorsal view . . 6 

2. Nerve-muscle preparation 7 

3. Muscle clamp, stand, and nerve-holder .... 8 

4. Tension indicator 25 

5. Stage electrometer . 38 

6. Long rheochord 43 

7. Square rheochord 44 

8. Simple key 45 

9. Short-circuiting key 46 

11. Pole-changer, early form . 49 

12. Rocking key 50 

14. Inductorium 54 

15. Platinum electrodes 65 

16. Flat-jawed clamp and round-jawed clamp .... 66 

17. Double clamp 6Q 

19. Long paper kymograph 82 

20. Smoker 84 

21. Light muscle lever 86 

22. Tuning fork 87 

23. Non-polarizable electrodes 94 

24. Moist chamber 95 

25. Hind limb of frog, anterior view 99 

25. Gaskell clamp 103 

26. Electro-magnetic signal 105 

28. Frog board 112 



XXIV ILLUSTRATIONS 

Fig. Page 

35. Motor points on the anterior surface of the forearm 

and hand 128 

36. Motor points on the posterior surface of the forearm 129 

and hand 

38. Brass electrodes 132 

42. Gas chamber, with bottle for generating carbon 

dioxide 172 

43. Sartorius 181 

44. Gracilis 183 

48. Scheme of myomeres in a parallel- fibred muscle . . 298 

49. Scheme of myomeres in an oblique section . . . 299 

50. Vibrating interrupter 303 

51. Vibrating interrupter arranged to make one contact 

per second . 304 

53. Heart lever * . 311 

54. Scheme of differential rheotome 313 

58. Volume tube 332 

59. Muscle warmer 343 

60. Heavy muscle lever 351 

61. Ergograph 354 

62. Work adder 359 

63. Lantern and optical box 404 

65. Reduced eye 459 

67. Respiration scheme 504 

68. Quantitative circulation scheme 512 

69. Mercury manometer 523 

70. Sphygmograph 527 

71. Sphygmograph tambour ......... 528 

72. Scheme of sympathetic nerve in frog 556 

73. Scheme of cervical nerves in frog 558 

74. View of brain of frog from above 565 



PART I 

THE GENERAL PROPERTIES OF LIVING 
TISSUES 



PART I 

THE GENERAL PROPERTIES OF 
LIVING TISSUES 



INTRODUCTION 

Until recent times it was believed that many of 
the compounds found in the tissues of animals 
and plants could be made only by the action of 
organized, i. e. living matter. Such compounds 
were called organic to distinguish them from 
those found in inorganic or inanimate nature. 
The forces producing organic compounds were 
thought to be partly the ordinary chemical 
and physical processes known to science, and 
partly certain mystical agencies termed vital 
forces. The great discovery of Wohler in 
1828 that urea (C02NH 3 ), a typical organic 
compound, could be made synthetically in the 
laboratory, overthrew this conception and was 
the beginning of a long and fruitful struggle to 



4 GENERAL PROPERTIES OF LIVING TISSUES 

bring the phenomena of living matter within 
the operation of chemical and physical laws 
without recourse to the supernatural and occult. 
According to this new, unified view of nature, 
which is the foundation of modern physiology, 
all phenomena, whether animate or inanimate, 
are alike the expression of chemical and physi- 
cal processes, some known, some unknown, none 
of which is fundamentally different from the 
rest. 

The physiologist, therefore, now looks upon 
the reactions of living matter with the eye of 
the physicist, and it is of the first importance 
to beginners in physiology to acquire this point 
of view. To this end it is desirable to consider 
living tissues from the standpoint of energy and 
to divide, even imperfectly, the functions to be 
studied into those that have to do with the 
income of energy and those that are active in 
its outgo. These studies cannot, however, be 
profitably undertaken without some acquaint- 
ance with the general properties of living tissues, 
such as irritability and contractility. 

We shall begin, therefore, by examining a 
motor nerve and the muscle in which its fibres 
are distributed. 

The Nerve-Muscle Preparation. — Wrap the 
frog in the cloth, the head out. Pass one blade 



INTRODUCTION 5 

of the stout scissors between the jaws. Bring 
this blade to the angle of the jaw, the other 
blade over the junction of the head and trunk. 
Cut off the skull with a single closure of the 
scissors. Thrust the pithing wire into the cranial 
cavity and then into the vertebral canal, destroy- 
ing the brain and spinal cord. The frog ceases 
to move; the muscles are relaxed. Divide the 
body transversely behind the fore limbs. Ee- 
move the viscera. Seize the spinal column with 
the finger and thumb of one hand, and the 
skin of the back with the other hand, covered 
with a cloth to prevent slipping. Draw the 
hind limbs out of the skin. Lay the limbs 
down, back uppermost, upon a clean glass 
plate, which the outside of the frog's skin has 
not touched. The skin of the frog, like that of 
the salamander and some other batrachians, is 
provided with a protective secretion injurious to 
sensitive tissues. Note on the outside of the 
thigh the triceps femoris muscle ; on the median 
side, the semi-membranosus ; between these, the 
narrow biceps femoris. (Fig. 1.) Cautiously di- 
vide the connective tissue between the semi- 
membranosus and the biceps femoris. On 
drawing these muscles apart, the sciatic nerve 
and the femoral vessels will be seen. Clear the 
nerve with scissors and forceps from the knee 



GENERAL PROPERTIES OF LIVING TISSUES 



to the vertebral column. The nerve itself should 
not be touched with the instruments. Near the 
pelvis it will be necessary to divide the pyriform 
and the iliococcygeal muscles: carefully avoid 

the nerve while do- 
ing this. 

With the forceps 
lift the tip of the 
urostyle (the 10 th 
vertebra, a long, slen- 
der bone which forms 
the caudal end of the 
vertebral column) 
and remove the bone 
with the stout scissors 
as far as the 9th 
vertebra. Divide the 
spinal column trans- 
versely between the 
6th and 7th vertebrae. 
)g back 
down. Bisect length- 
wise the 7th, 8th, and 9th vertebrae. Grasp 
the half from which the prepared nerve springs 
and lift it gently, freeing the nerve with the 
scissors down to the kuee. 

Pass now to the leg. Cut through the Achil- 
les tendon of the gastrocnemius muscle below 




Fig. 1. Muscles of left hind limb of 
frog, dorsal view (Eeker and Wieders- Tinv-i-. flip 
heim). 



INTRODUCTION 




the thickening at the heel. Free the muscle up 

to its origin from the femur, taking care not to 

harm the branch of the nerve which enters the 

muscle on its posterior surface near the knee. 

Cut through the tibia about one 

centimetre from the knee-joint. 

Clear away the muscles of the 

thigh from the lower end of the 

femur, avoiding the sciatic nerve. 

Cut through the femur about 

its middle. (Fig. 2.) Lay the 

sciatic nerve for safety along the 

gastrocnemius muscle. Fasten 

the lower fragment of the femur Fi s- 2 - Nerve-mus- 

cle preparation ; gas- 
in the jaWS Of the muscle clamp, trocnemius muscle 
-r . , , , , , . . , and sciatic nerve. F, 

Let the whole nerve rest with- end of femur ;n sei- 
out stretching on the adjustable S^'iS 
plate or nerve-holder, the filter ment of smaller ten - 

don of gastrocnemius 

paper Covering which should be to femur (Handbook 

. , . , , , . for the Physiological 

moistened with normal saline Laboratory). 
solution (0.6 per cent ISTaCl). 
Take care that the nerve does not dry between 
the nerve-holder and the muscle. (Fig. 3.) The 
filter paper should reach from the nerve-holder 
to the muscle. 

Preliminary Considerations regarding Energy, 
Stimulation, and Irritability. — Pinch the muscle 
sharply with the forceps. 



8 GENERAL PROPERTIES OF LIVING TISSUES 

The muscle passes into the active state; it 
shortens and thickens. The foot, which is rela- 










Fig. 3. The muscle clamp, stand, and nerve-holder. The nerve-holder 
supports the sciatic nerve, together with the portion of the spinal column 
from which it springs. The handle of the nerve-holder is of thick lead 
wire which may be bent as desired. The binding post on the muscle clamp 
provides electrical connection with the upper end of the muscle. 

tively less fixed than the leg, is extended. The 
contraction is followed by a slower relaxation or 
return to the original form. 



INTRODUCTION 9 

Observe that the mechanical act of pinching 
caused the resting muscle to become active. Its 
stored energy was transformed into external, 
mechanical work, i. e„ the moving of the foot. 
Not all of the energy set free takes this easily 
visible form. It will be shown later that much 
of it is made active as molecular motion, in the 
form of heat, chemical action, and electricity. 
Agents which occasion a transformation of 
energy within the living body are termed stim- 
uli, and tissues which convert energy of one 
form into energy of another in consequence of 
stimulation are said to be irritable. All living 
tissues are alike irritable, but the form in which 
their kinetic or active energy appears differs 
with the nature of the tissue. The contrast 
between muscle and nerve in this respect is 
especially instructive. 

Pinch the end of the nerve. 

No change will be seen in the nerve, but the 
muscle will contract. 

Thus, while the most conspicuous form which 
the energy of muscle takes, when set free, is 
mechanical, the active nerve does not alter its 
form, but spends its energy in a molecular 
change, the nerve impulse, which passes from 
point to point along the nerve to the muscle, 
or gland, or other structure connected function- 



10 GENERAL PROPERTIES OF LIVING TISSUES 

ally to the nerve. The effect produced by 
the nerve impulse depends on the nature of 
the tissue in which the nerve ends ; for ex- 
ample, the energy set free in secreting glands 
is especially chemical; that set free in the 
electrical organ of Torpedo is especially elec- 
trical. In considering these illustrations of the 
ways in which the energy of living tissue may 
be set free, however, two facts should always 
be kept in mind ; first, that by far the greater 
part of the stored energy of the body is set 
free as heat; and secondly, that while the sev- 
eral tissues are characterized by the especial 
prominence of some one form of energy, as 
contractility in the case of muscle, and the 
production and conveyance of a nerve impulse 
in the case of nerve, yet the transformation of 
energy in each tissue is a complex process, 
many steps of which, for example heat and 
chemical action, are common to all living 
substance. 

We have made, then, the fundamental obser- 
vation that an adequate stimulus will occasion 
in muscle a conversion of latent energy into 
mechanical change in form and in the nerve a 
molecular change that passes along the nerve as 
a nerve impulse. We must now examine sys- 
tematically the usual methods of exciting the 



INTRODUCTION 11 

transformation of energy and inquire concerning 
their effect on muscle and nerve. 

Apparatus 

Normal saline. Bowl. Cloth. Pithing wire. Scissors. 
Forceps. Pipette. Glass plate. Cement. Foil. Nerve- 
holder (filter paper). Muscle clamp. Stand. Frog. 



12 GENERAL PROPERTIES OF LIVING TISSUES 



II 

METHODS OF ELECTRICAL STIMULATION 
Introduction 

The stimulus most usually employed in the 
laboratory is electricity, because electricity will 
stimulate when used in quantities which do not 
destroy the tissues, as do many mechanical, 
chemical, and thermal stimuli, and because the 
intensity and duration of the electrical stimulus 
can be graduated with accuracy. It will be 
necessary, therefore, to examine with especial 
care the methods and the results of electrical 
stimulation. These matters are involved with 
problems of ionisation, surface tension, osmosis, 
and other molecular actions highly important 
in many fields of physiology. Such interde- 
pendent phenomena cannot be studied profitably 
without working hypotheses that shall attempt 
to relate them as forms of energy. 

Kinetic Theory. — The particles of a gas, the 
simplest state in which matter exists, are identi- 
cal with its chemical molecules. These particles 



METHODS OF ELECTRICAL STIMULATION 13 

are assumed by Clausius and Maxwell to be in 
constant rapid motion in all directions. It is 
this motion which causes the "disappearance" 
of a gas " set free " in the open air. The mole- 
cules of air are also in rapid motion and fre- 
quently collide with each other and with those 
of the escaping gas, but the air molecules are 
far from filling the space in which they move 
and the molecules of gas rapidly pass off be- 
tween them. In their flight, they strike with 
a measurable force whatever opposes them, be 
it another flying molecule or some boundary 
wall. The force of the blow is the " pressure " 
of the molecule. If the gas be confined by an 
impermeable wall, that is, a wall the inevitable 
openings in which are too small for the gas 
molecules to pass, the sum of the blows of the 
molecules dashing against this wall will be the 
total pressure of the gas. 

Partial pressure. — If the molecules of a second 
gas be within the containing vessel, they also 
will strike the boundary. The force of their 
blows will be entirely independent of the force 
of the blows struck by the molecules of the 
first gas. It is as if black and white balls were 
thrown at the same time against a wall ; their 
blows would be independent of each other. 

The molecules of gas and the contininu: walls 



14 GENERAL PROPERTIES OF LIVING TISSUES 

are assumed to be perfectly elastic, so that the 
motion of a molecule is not lost when it collides 
with another molecule or strikes the wall; the 
direction of the flight is changed but the swift- 
ness is unimpaired. The speed of the molecules 
of a gas is inversely proportional to the square 
root of its density. At 0° C. the molecule of 
oxygen moves at the rate of almost eighteen 
miles per minute. 

Diffusion of gases. — The molecules of two 
gases moving in the same space will intermix 
or " diffuse," but the rate will be surprisingly 
slow, for at ordinary pressures the molecules of 
gases are so near together that they cannot move 
far without colliding and rebounding. Their prog- 
ress in any one direction is thus greatly hindered. 

Every particle of matter attracts every other 
particle. Van der Waal assumes that with gases 
this attraction is proportional to the square of 
the density of the gas. Where the density is 
slight, that is, where there are few molecules in 
proportion to the space in which they move, this 
attraction need not be taken into account, but 
where the confining space is small, thus crowd- 
ing the molecules together, this attraction be- 
comes important. It is still more important in 
the case of liquids, for in liquids the molecules 
are much nearer than in a gas. 



METHODS OF ELECTRICAL STIMULATION 15 

Vapor pressure. — Were it not for the attrac- 
tive or cohesive force just mentioned, the mole- 
cules of a liquid would rapidly pass into the 
space surrounding the liquid and the liquid 
would soon disappear (evaporation). But the 
molecules are so close together that their attrac- 
tion for each other largely prevents escape. 
Nevertheless, the motion of many of the mole- 
cules at or near the surface of the liquid is 
sufficient to break through this force of cohesion. 
These molecules escape and their places are 
taken by molecules which may in turn escape. 
Thus evaporation proceeds. In the vapor above 
the liquid the escaping molecules collide with 
other molecules and may be driven by the recoil 
back into the liquid. If the liquid be in a 
confined space, the number of vapor molecules 
recoiling into the liquid will increase, partly 
because they are brought nearer together and 
collisions are thus more frequent and partly 
because the molecules rebound from the con- 
taining wall. When the number of molecules 
returning equals the number leaving the liquid, 
the vapor and the liquid are in equilibrium 
(saturation). In other words, the vapor tension 
or pressure or force with which the liquid mole- 
cules tend to leave the liquid is balanced by the 
gas pressure or force with which the gas mole- 



16 GENERAL PROPERTIES OF LIVING TISSUES 

cules strike against the liquid. As the speed 
of the molecules and therefore their power to 
escape from the liquid rises with the tempera- 
ture, the vapor pressure will also rise with the 
temperature. 

Solution of a gas in a liquid. — A liquid 
brought near a gas is struck by many of the 
moving molecules of the gas. Some of these are 
held by the attractive force of the liquid. Some 
will at length escape. Finally, as the number 
of molecules striking the surface of the liquid 
remains constant at the same pressure, the gas 
molecules leaving the liquid will equal the number 
entering (saturation). 

Solution of a solid in a liquid. — When a crys- 
talline solid is placed in a liquid solvent, particles 
escape from the solid and enter the liquid. Some 
of these particles again enter the solid and are 
bound by it. Saturation is reached when the 
number of particles entering and leaving the 
solid is equal. 

Solution tension. — The force with which the 
particles of the solid pass into the solvent is 
termed the solution tension. There is equili- 
brium, i. e. saturation, when the solution tension 
is balanced by the force with which the particles 
in the solvent return to the solid. 

Osmotic Pressure. — It has been found that 



METHODS OF ELECTRICAL STIMULATION 17 

hydrogen gas will pass through the metal palla- 
dium when the metal is heated to 200° C. Nitro- 
gen will not pass through. Palladium at 200° C. 
is therefore said to be semi-permeable, i. e. it is per- 
meable to one gas, but not to another. If a tube 
of palladium at 200° containing nitrogen gas at 
a pressure of one half atmosphere be placed in a 
vessel containing hydrogen gas at a pressure of 
one atmosphere, the hydrogen will pass through 
the palladium into the tube until the pressure 
of the hydrogen inside equals that outside the 
tube, namely, one atmosphere. The pressure in 
the tube will now be almost one and one half 
atmospheres, which is the sum of the partial 
pressure of the nitrogen (one half atmosphere) 
and the partial pressure of the hydrogen (one 
atmosphere), less an error due chiefly to the im- 
perfect permeability of the palladium. Thus the 
pressure on one side of the palladium will be 
higher than that on the other side, as may be 
shown by connecting the tube with a manometer. 

Substances in solution may exert a force like 
the partial pressure of a gas. This force is called 
osmotic pressure. 

Osmotic pressure is measured most readily by 
the aid of semi-permeable membranes, first used 
for this purpose by Pfeffer. For demonstration 
they may be made as follows. Wash a porcelain 



18 GENERAL PROPERTIES OF LIVING TISSUES 

diffusion bulb twenty-four hours in running 
water. Dry the bulb and coat its neck inside 
and out with paraffin ; when this has become 
firm, fill the bulb to above the lower edge of the 
paraffin with solution of copper sulphate (2.5 gm. 
per litre). Place the bulb in a beaker and pour 
in a solution of potassium ferrocyanide (2.1 gm. 
per litre) until the lower edge of the paraffin is 
covered. Keep the bulb in this solution over 
night. Where the two solutions meet within the 
clay wall a precipitation membrane of copper 
ferrocyanide will form. This membrane is sup- 
ported by the clay wall. Pour out the contents 
of the bulb and rinse with cold distilled water. 
Through such precipitation membranes water 
and some other solvents will readily pass, while 
many salts dissolved in the solvent are kept 
back. 

Fill the bulb with one per cent solution of 
cane sugar. Insert in the neck of the bulb a 
tightly fitting rubber stopper pierced by a small- 
bore glass tube about ten feet long. Stand the 
bulb in distilled water and support the long 
tube in suitable clamps. The sugar will not pass 
out through the membrane, but water will pass 
through it into the bulb, and the solution will 
rise in the tube at the rate of several inches an 
hour. The rate is slow because the friction in 



METHODS OF ELECTRICAL STIMULATION 19 

the artificial membrane is great ; the osmosis of 
salts through living membranes may be very rapid. 
When the liquid in the tube is high enough to 
balance the force with which the water would 
pass through the membrane, the flow ceases. 
The difference in water level is the osmotic 
pressure, the analogue of gas pressure. The maxi- 
mum osmotic pressure is so great that only perfect 
semi-permeable membranes will support it. 

It will be obvious upon reflection that osmotic 
pressure must be independent of the semi-per- 
meable membrane. The solvent is continuous 
through the membrane. The only function of 
the membrane is to render the osmotic pressure 
visible. 

With constant temperature the osmotic pres- 
sure is nearly proportional to the concentration 
of the solution. 



Eatio. 



53.5 
50.8 
55.4 
52.1 
51.3 

The osmotic pressure increases as the tempera- 
ture rises. 



Concentration 


Osmotic pressure 


of solution of 


in centimetres 


cane-sugar. 


of mercury. 


Per cent. 




1 


53.5 


2 


101.6 


2.74 


151.8 


4 


208.2 


6 


307.5 



20 GENERAL PROPERTIES OF LIVING TISSUES 

Ten years after these observations were pub- 
lished by Pfeffer, Van't Hoff pointed out the 
analogy between osmotic pressure and gas pres- 
sure. It has just been shown that, if the tem- 
perature be constant, the osmotic pressure is 
proportional to the amount of dissolved substance 
in a given volume ; thus the osmotic pressure 
of a solution, like that of a gas, varies inversely 
with the pressure. Moreover, the osmotic pres- 
sure, like gas pressure, increases with the tempera- 
ture. Pfeffer observed that the osmotic pressure 
of a cane sugar solution at 14.2° C. was 51 cm. 
Hg. Assuming that the osmotic pressure, like 
gas pressure, is proportional to the absolute 
temperature, Pfeffer then determined by calcula- 
tion that the osmotic pressure of this same 
solution at 32.0° C. should be 54.2 cm. Actual 
observation gave 54.4 cm. 

In short, the osmotic pressure of a dissolved 
substance is numerically equal to the pressure 
which the substance would exert were it present 
as a gas. 

Plasmolysis. Isotony. — The cells of Trades- 
can tia discolor possess a strong outer envelope 
permeable by both water and salts, and a thin 
inner envelope permeable by water, but not by 
salts. The cell is rilled with an aqueous solution 
of glucose, salts of malic acid, etc. The osmotic 



METHODS OF ELECTRICAL STIMULATION 21 

pressure of the contents is from four to six 
atmospheres. When the cell is placed in water, 
the water penetrates both envelopes and the cell 
swells so far as the resistant outer envelope 
may permit. In a concentrated salt solution, 
the osmotic pressure pushes the inner envelope 
away from the outer envelope, contracting the 
volume of the cell contents (plasmolysis), and 
water leaves the cell until the concentration of 
the cell contents equals that of the surrounding 
solution. Solutions whose concentration is such 
that cells immersed in them are not deformed 
must possess the same osmotic pressure. Such 
solutions are termed isotonic or isosmotic. 

Estimation of Osmotic Pressure in the Blood 
Serum. 1. The method of de Fries. 1 — Make a 
section along the midrib of the violet side of 
the leaf of Tradescantia discolor and two other 
sections one on each side, parallel to and about 
2 mm. from the first. Now make transverse 
sections across the three vertical sections about 
5 mm. apart, and a final very thin section paral- 
lel to the surface. Place some of these thin tan- 
gential sections in the serum diluted with 20 per 
cent of water, and others in salt solutions of 
different concentrations (0.60, 0.65, 0.70, 0.75, 0.80 

1 de Vries: Zeitschrift fur physikalisclie Chemie, 1888, ii, 
p. 419. 



22 GENERAL PROPERTIES OF LIVING TISSUES 

per cent). From time to time remove the sec- 
tions and observe under the microscope whether 
plasmolysis is present. The serous fluid that 
causes plasmolysis in half the cells immersed 
in it, is isotonic or " normal " with the salt solu- 
tion having the same effect. 

For example, if there were used 5 c.c. serum 
+ 1 c.c. water with 0.8 per cent solution of sodium 
chloride, the original serum would be isotonic 

5 + 1 
with a sodium chloride solution of x 0.8 

o 
= 0.96 per cent. 

Should the osmotic pressure of the serum be 
too slight to call forth plasmolysis in the cells 
employed, add to the serum measured quantities 
of a strong saline solution, e. g. 5 per cent sodium 
chloride solution. 1 

2. The Hood- corpuscle method of Hamburger? 
— Place 5 c.c. serum in each of six test-tubes. 
To these add from a burette 3.1, 3.0, 2.9, 2.8, 2.7, 
and 2.6 c.c. water, respectively. Into each tube 
let fall three drops of defibrinated blood, and mix 

1 Hamburger : Osmotischer Druck und Ioneulehre, 1902, 
i, p. 438. 

The cells of Tradescantia cannot be used for the measure- 
ment of osmotic pressure in acid solutions. For the urine, the 
cells of Begonia manicata should be used. 

2 Hamburger : Loc. cit. pp. 185 and 439. Also Archiv fur 
Physiologie, 1887, p. 31. 



METHODS OF ELECTRICAL STIMULATION 23 

by shaking, taking care that the mixture does 
not foam too much. 

In each of six other test-tubes place 8 c.c. 
sodium chloride solution of 0.62, 0.61, 0.60, 0.59, 
0.58, and 0.57 per cent, respectively. Into each 
tube let fall three drops of the same defibrinated 
blood. Mix as before. After some hours the 
red corpuscles will have settled to the bottom 
in all the tubes. 

In the first series the clear fluid will be red 
in some of the tubes. For example, the fluid in 
the tubes diluted with 3.1, 3.0, and 2.9 c.c. water 
may be red, while in the three other tubes it may 
not be red. In this case the mixture of 5 c.c. 
serum + 2.9 c.c. water has caused the haemo- 
globin to escape from the corpuscles ("laked" 
the blood), while the mixture of 5 c.c. serum 
+ 2.8 c.c. water has not accomplished this. 

If the tubes with salt solution be now exam- 
ined, escaped haemoglobin will be found only in 
the 0.58 per cent and the weaker solutions. Con- 

O Q I O O 

sequently the mixture of 5 c.c. serum H — : — x — — 

water is isotonic with a sodium chloride solution 

. 0.59 + 0.85 n ror 
of ^ — 0.585 per cent. Hence the un- 
diluted serum is isotonic with a sodium chloride 

5 _j_ 2.85 
solution of p^ — x 0.585 = 0.92 per cent. 



24 GENERAL PROPERTIES OF LIVING TISSUES 

In a solution of this concentration the red blood- 
corpuscles of mammals are in osmotic equi- 
librium. 1 The isotonic (isosmotic or normal) 

1 In this calculation it is assumed that the osmotic pressure 
is proportional to the concentration. This is not strictly cor- 
rect. When serum is diluted with an equal volume of water, 
the osmotic pressure of the resulting liquid is not merely half 
so large as before, but is somewhat greater than one half the 
original pressure. For when the water is added, a part of the 
molecules not yet dissociated are split into ions and each ion 
has an osmotic pressure equal to that of an undissociated mole- 
cule. If the serum upon dilution with water followed the 
same dissociation curve as the sodium chloride solution of 0.92 
per cent, the above method of calculation would be strictly 
correct. This is, however, not the case ; on the contrary, the 
dissociation curves separate from each other. But this devia- 
tion, in the case of the dilutions considered here, lies within 
the limit of errors of observation, probably because the osmotic 
pressure of the serum is due chiefly to sodium chloride (Ham- 
burger, p. 186). 

The above calculation also leaves out of account the fact 
that the blood-corpuscles are permeable for anions. It is evi- 
dent that the exchange of ions between blood-corpuscles and 
surrounding liquid will differ according as this liquid is dilute 
serum or pure sodium chloride solution. For the partial ten- 
sion of the ions in the two solutions is not the same. The 
partial pressure of the CI" ions in the 0.6 per cent sodium 
chloride solution is greater than in the serum diluted with 60 
per cent water; while in the serum there is a pressure of 
CO"' ions, lacking in the sodium chloride solution. Moreover, 
the blood-corpuscles placed in these liquids acquire a different 
composition. The osmotic pi*essure of the blood-corpuscles is 
increased by immersion in sodium chloride solution. 

Dissociation and permeability act with opposite sign, balanc- 
ing each other. That the blood-corpuscle method is practically 



METHODS OF ELECTRICAL STIMULATION 



25 



concentration for the corpuscles of frog's blood is 
0.6 per cent. 

Surface Tension. — The osmotic pressure of 
solutions is very great. In the ordinary reagents 
of the laboratory it amounts to many atmos- 
pheres. Obviously, such solutions could not be 
kept in thin glass beakers or 
bottles were these enormous 
pressures not restrained by 
some opposing force. This op- 
posing force is surface tension, 
which acts with a pressure of 
probably hundreds of atmos- 
pheres upon the free surface of 
a liquid, whether that surface 
be bounded by air or glass. 
The semi-permeable membrane 
is filled with liquid, and there- 
fore does not present a free 
surface. 

1. A thick wire is bent to enclose a right- 
angled space and the end prolonged for a handle. 
(Fig. 1.) A very fine slack-wire divides the space 
in halves. 




.Fig. 4. The tension 
indicator. 



accurate may be shown by comparison with the method of 
estimating osmotic pressure by the depression in the freezing- 
point of the solution, which is proportional to the concentration 
of the solution (p. 439). 



26 GENERAL PROPERTIES OF LIVING TISSUES 

Dip the tension indicator into a soap solution. 

A thin layer of the solution will span the 
frame on both sides of the dividing wire. The 
tension of the membrane on one side of the di- 
viding wire compensates that on the other and 
the wire will not move. 

Hold the frame in a vertical position. The 
cross wire will sink slightly, owing to the force 
of gravity. Absorb the lower membrane with 
filter paper. 

The cross wire will at once be lifted against 
the force of gravity by the surface tension of the 
remaining membrane. Destroy the remaining 
membrane and the wire will fall again. 

2. Strew lycopodium 1 upon a water surface. 
In the centre place a few drops of alcohol. 

The lycopodium will be driven in all direc- 
tions. The surface tension of alcohol is less 
than that of water. The water-air surface and 
the alcohol-air surface are therefore not in 
equilibrium. The water-air surface contracts 
violently, and the alcohol-air surface expands, 
producing the strong currents made visible by 
the motion of the lycopodium. 

Electrolysis. — 1. Connect two dry cells in 
series (carbon of one cell connected with zinc of 
other). Attach wires to the terminal zinc and 

1 Be careful not to bring the rycopodiimi near a flame. 



METHODS OF ELECTRICAL STIMULATION 27 

carbon. Touch the ends of the wires together. 
An electric current passes, as evidenced by the 
spark when the contact is made or broken, but 
no material change can be observed in the me- 
tallic conductor. 

2. Place two pieces of platinum foil in a solu- 
tion of copper sulphate and connect them to the 
terminal zinc and carbon as before. Copper will 
be deposited on the platinum connected with the 
zinc, and oxygen will be deposited on the plati- 
num connected with the carbon. Thus the 
passage of the current through the conducting 
solution or electrolyte has caused a change in 
the solution, evidenced by a movement of pon- 
derable matter. 

Faraday discovered that the quantity of matter 
moved by the current was always proportional 
to the quantity of the current, independent of 
its strength or speed. In the electrolysis of 
hydrochloric acid 96,500 coulombs x will set free 
1 gm. of hydrogen. Faraday also discovered 
that the same quantity of current (96,500 cou- 
lombs) which carries 1 gm. of hydrogen will 
carry the chemical equivalent of any other sub- 

1 A coulomb (ampere) of electricity is the quantity of cur- 
rent which, when passed through a solution of silver nitrate in 
water, deposits silver on the cathode, or negative pole, at the 
rate of 0.001118 gram per second. 



28 GENERAL PROPERTIES OF LIVING TISSUES 

stance, for example 35.5 gm. of chlorine. In the 
above experiment on the electrolysis of copper 
sulphate solution, each 31.5 grams of copper 
moved to the zinc pole requires the passage of 
exactly 96,500 coulombs. The particles of matter 
travelling in the solution toward the anode were 
called by Faraday the anions and those travel- 
ling toward the cathode were called cations. On 
reaching the poles the ions give up their electric 
charge and resume their simple chemical nature. 
Thus each 31.5 grams of copper ions, on reaching 
the cathode, gives up 96,500 coulombs of electric- 
ity and becomes ordinary copper again, and each 
96 grams of sulphate ions gives up 96,500 cou- 
lombs and becomes the ordinary radical S0 4 . 
This radical cannot exist uncombined in water, 
but forms sulphuric acid. S0 4 + H 2 = H 2 S0 4 
+ O. Thus the liquid around the anode becomes 
acid, and actual measurement has shown that the 
quantity of sulphuric acid formed at the anode 
is exactly equivalent to the quantity of copper 
deposited on the cathode. 

The ions move very slowly. The high vis- 
cosity or internal friction of the liquid opposes a 
great resistance to the movement of ions as well 
as to the osmosis of dissolved substances. To 
drive 1 gm. of hydrion (OH) through pure water 
at the rate of 1 cm. per second, a force equal to 



METHODS OF ELECTRICAL STIMULATION 29 

320,000 tons' weight is required. To diffuse 
1 gm. urea through pure water at the rate of 
1 cm. per second, 40,000 tons' weight is required. 
In dilute aqueous solutions at 18° C. a difference 
of potential of 1 volt between electrodes 1 cm. 
apart will drive the cation H 10.8 cm. per hour, 
the cation Na 1.26 cm., the anion OH 5.6 cm., 
and the anion CI 2.12 cm. per hour. 

As the ions move so slowly and as the products 
of electrolysis appear at each electrode the 
moment the current is made, it is evident that 
the ions which immediately appear at the anode 
cannot be derived from the same molecules as the 
ions which simultaneously appear at the cathode. 

" Clausius explains this in the following way : 
According to the theory of molecular motion, of 
which he has himself been the chief founder, 
every molecule of the fluid is moving in an ex- 
ceedingly irregular manner, being driven first one 
way and then another by the impacts of other 
molecules which are also in a state of agitation. 

" This molecular agitation goes on at all times 
independently of the action of electromotive force. 
The diffusion of one fluid through another is 
brought about by this molecular agitation, which 
increases in velocity as the temperature rises. The 
agitation being exceedingly irregular, the encoun- 
ters of the molecules take place with various 



30 GENERAL PROPERTIES OF LIVING TISSUES 

degrees of violence, and it is probable that even at 
low temperatures some of the encounters are so 
violent that one or both of the compound molecules 
are split up into their constituents. Each of these 
constituent molecules now knocks about among 
the rest till it meets with another molecule of 
the opposite kind, and unites with it to form a 
new molecule of the compound. In every com- 
pound, therefore, a certain proportion of the 
molecules at any instant are broken up into their 
constituent atoms. 

" Now Clausius supposes that it is on the con- 
stituent molecules in their intervals of freedom 
that the electromotive force acts, deflecting them 
slightly from the paths they would otherwise 
have followed, and causing the positive constit- 
uents to travel, on the whole, more in the positive 
than in the negative direction, and the negative 
constituents more in the negative direction than 
in the positive. The electromotive force, there- 
fore, does not produce the disruptions and reunions 
of the molecules, but, finding these disruptions 
and reunions already going on, it influences the 
motion of the constituents during their intervals 
of freedom." 1 

1 Quoted from Clerk Maxwell by Walker in his admirable 
"Introduction to Physical Chemistry," a book to which the 
present writer is much indebted. 



METHODS OF ELECTRICAL STIMULATION 31 

Views of Arrhenius. — It was Arrhenius who 
made these ideas regarding the dissociation of 
the molecules of solutions into ions quantitative 
and thus precise. Feeble electrolytes, i. e. poor 
conductors of electricity, are but slightly dis- 
sociated, whereas solutions that readily conduct 
electricity are largely dissociated. Ionisation 
may be measured by the degree of conductivity. 
Undissociated molecules carry no electricity. Each 
univalent ion has the same load : 96,500 coulombs. 

Conductivity depends on the number of the 
ions and upon their speed. In this connection 
the following observation is of interest. If suc- 
cessive quantities of pure water be added to a 
salt solution, the conductivity will increase as 
the dilution increases. The first factor to be 
considered here is the viscosity of the solution, 
for the viscosity determines the resistance of the 
solution to the passage of ions, and thus determines 
the speed of the ions. As the addition of water 
continues a point is soon reached at which the 
amount of water in the solution is so great in 
relation to the amount of salt that the water may 
be regarded practically as pure. The addition 
of more water should not then appreciably affect 
the viscosity and thus the speed of the ions. If 
the conductivity were related solely to the speed 
of the ions, the conductivity should not then 



32 GENERAL PROPERTIES OF LIVING TISSUES 

increase upon this further addition of water. 
Observation shows that it does increase. It 
must therefore depend on the degree of dissocia- 
tion, i. c. the number of ions. 

When the solution is heated, its viscosity and 
thus its fluid friction diminishes ; the ions pass 
through it with less difficulty and the conduc- 
tivity rises. Non-conducting substances added 
to aqueous solutions may affect both the number 
and the speed of the ions. The first additions 
of alcohrjl to a dilute solution increase the vis- 
cidity, and lessen the speed of the ions : after a 
certain limit, further additions have little effect 
on the speed, but markedly lessen the number 
of the ions, i e. the degree of ionisation or dis- 
sociation. Comparisons of electrical conductivity 
in solutions of different concentration can be 
made only when the rate at which the ions 
move remains the same ; in other words, the 
salt, the solvent, and the temperature must be 
the same in the two solutions. 

Electrolytic solution Pressure. — When a salt 
is placed in water it dissolves until its solution 
pressure or tendency to pass into solution is 
balanced by the osmotic pressure of the dissolved 
particles. If the osmotic pressure exceed the 
solution pressure, salt will be deposited. As 
the salt dissolves, positive and negative ions are 



METHODS OF ELECTRICAL STIMULATION 33 

formed in equivalent quantities, so that there is 
no difference in electrical pressure. 

When metallic zinc is placed in dilute sulphu- 
ric acid, it dissolves, and positively charged zinc 
ions enter the solvent, but no negative ions are 
formed at the same time. The solution next 
the metal becomes statically charged with posi- 
tive electricity, and in consequence the zinc itself 
becomes negatively charged. The electrical stress 
thereby produced compensates the difference 
between the osmotic pressure of the zinc ion and 
the electrolytic solution pressure of the zinc. 

When copper is placed in a solution of copper 
sulphate, the osmotic pressure of the metal ion 
exceeds the electrolytic solution pressure of the 
metal and metallic copper is deposited on the 
surface of the electrode. The metal becomes 
positively charged and the solution negatively 
charged through the sulphanions that gather at 
the layer of solution next the metal. This pro- 
cess continues until the electrical stress balances 
the difference between the actual osmotic pres- 
sure and the electrolytic solution pressure. 

The electrical double layer about each elec- 
trode is of only molecular thickness, so that the 
solution or deposition of an extremely small 
quantity of metal is sufficient to establish equi- 
librium. 

3 



34 GENERAL PROPERTIES OF LIVING TISSUES 

In galvanic cells, in which two metals are 
immersed in one or more electrolytes, there are 
three sources of electromotive force : the junc- 
tion of the metals with the electrolytes, the 
junction of the two metallic conductors, and the 
junction of the electrolytes. The junction of 
the metals with the electrolytes is the principal 
source ; the electromotive force produced by the 
junction of the metals is slight, and the ions of 
different neutral salts move at not far from the 
same speed, so that the electromotive force at the 
junction of the electrolytes is also relatively 
small. 



The Electrometer, the Kheocord, and 
the Cell 

In order to study differences in electrical 
potential, 1 a galvanometer or some other elec- 

1 The difference of potential may be compared to the differ- 
ence of water level between a reservoir and its distributing 
pipes. It produces an electromotive force, comparable to the 
force which moves the water from the higher to the lower level. 
The unit of electrical pressure is the volt. The flow through 
an hydraulic system is measured by the quantity of water pass- 
ing any point in a given time ; similarly the quantity of elec- 
tricity is the amount that flows through a cross-section of the 
conductor in a given time. The unit of quantity is the ampere. 
Electricity passing through a conductor meets with a resistance 
which becomes greater as the cross-section of the conductor 



METHODS OF ELECTRICAL STIMULATION 35 

trometer is necessary. In the galvanometer, the 
points of different potential are connected by a 
coil of wire near which is suspended a magnet. 
When the circuit is completed, the electrical 
energy acts on the suspended magnet by induc- 
tion, and deflects it to an extent proportionate 
to the difference of potential. In the capillary 
electrometer, which is the electrometer preferred 
here, a capillary tube filled with mercury and 
sulphuric acid dips in a wider tube which con- 
tains sulphuric acid. The points the potential 
of which is to be measured are connected with 
the mercury and the acid respectively. When 
the connection is made, the tension of the sur- 
face of mercury in contact with the acid changes, 
causing the mercury to move in the capillary. 
The change in surface tension is proportional to 

diminishes, just as water can be forced more easily through 
wide channels than through narrow ones. The unit of electri- 
cal resistance is the ohm. The precise definition of these units 
is as follows : 

A volt is the electromotive force that, steadily applied to a 
conductor whose resistance is one international ohm, will pro- 
duce a current of one international ampere. The practical 
ampere {coulomb) is the unvarying current which, when passed 
through a solution of nitrate of silver in water, deposits silver 
on the cathode, or negative pole, at the rate of 0.001118 gram 
per second. The ohm is the resistance offered to an unvarying 
electrical current by a column of mercury at the temperature 
of melting ice, 14.4521 grams in mass, of a constant cross- 
sectional area, and of the length of 106.3 centimetres. 



36 GENERAL PROPERTIES OF LIVING TISSUES 

the difference in potential. The action of the 
instrument will be more clear from the follow- 
ing experiments. 

Surface Tension altered by Electrical Energy. — 
In a small porcelain evaporating dish place a 
globule of mercury about one inch in diameter. 

The cohesion of the mercury is stronger than 
the attraction between the mercury and porce- 
lain, — the mercury does not " wet " the porcelain. 
The free surface of the mercury is curved and 
not plane, as it would be were the molecules 
acted upon by the force of gravity alone. Obvi- 
ously the spreading of the mercury is resisted by 
some force that strives to make the drop spher- 
ical, i. e. to make the surface as small as possible. 

This force is called the surface tension. It is 
the attraction which the molecules beneath the 
surface exert on the side of the surface layer 
next them. The form of the drop is the result 
of the equilibrium between these opposing forces 
(Thomas Young, 1804). 

Cover the mercury one centimetre deep with 
5 per cent sulphuric acid. Note carefully the 
degree of convexity. Add a trace of potassium 
bichromate. The drop will flatten slightly. 

When a metal is placed in an electrolyte, a 
difference of potential is created at the surfaces 
in contact. If the metal is positive compared 



METHODS OF ELECTRICAL STIMULATION 37 

with the electrolyte, an immeasurably thin layer 
of positively electrified molecules may be said to 
coat its surface, and in the electrolyte a parallel 
layer of negatively electrified molecules will 
collect. On every side of the parallel layer 
electricity of the same sign will be repelled. In 
the case of a liquid metal, for example mercury, 
the form of the surface will be altered, for the 
repulsion of like electricities will tend to stretch 
the surface layer, and will thus oppose the sur- 
face tension. The new form which the surface 
will take is the equilibrium between the electri- 
cal energy and the surface tension (Helmholtz). 
If this equilibrium is changed by the introduc- 
tion of new electrical energy, the curvature of 
the surface will change (Henry). 

Fasten an iron wire in the muscle clamp and 
clamp the latter to the stand. Bring the wire 
over the mercury and lower the muscle clamp 
until the wire just touches the edge of the 
mercury. Fix the clamp in this position. 

The instant the two metals touch (iron and 
mercury in chromic acid solution) the existing 
difference of potential will be altered. The sur- 
face tension will thereby be increased and the 
globule will become more convex. This move- 
ment withdraws the margin of the globule from 
the iron and the globule flattens again, which 



38 GENERAL PROPERTIES OP LIVING TISSUES 

brings it again into contact with the iron. This 
play is repeated until the chromic acid is all 
reduced to chromic sulphate. 




Fig. 5. Stage electrometer; 1 about three-sevenths the actual size. A. 
Side view. B, Front view. 



The Electrometer. — The electrometer consists of 
a vertical tube drawn out at the lower end into a 
fine capillary and filled with mercury. (Fig. 5.) The 

1 Science, 1905, xxii, p. 602. 



METHODS OF ELECTEICAL STIMULATION 39 

upper end of the tube is joined to a cylinder in which 
a piston is moved by a screw, thus making pressure 
on the mercury column. The end of the capillary dips 
in a reservoir containing twenty per cent sulphuric 
acid. Platinum wires lead from the acid reservoir 
and the mercury in the capillary to convenient bind- 
ing posts. The platinum wire should never touch 
the acid, but should be protected by a covering of 
mercury. When mercury is placed in the vertical 
tube it enters the capillary until the weight of the 
column of mercury is balanced by the surface tension, 
which is inversely proportional to the diameter of the 
tube. If the capillary be now dipped in the reservoir 
containing the sulphuric acid, and the piston driven 
upward by its screw, mercury will be forced out of the 
capillary into the acid ; and on lowering the pressure 
the mercury will retreat within the capillary, drawing 
the acid after it. Numerous advantages are presented 
by this form of electrometer. It fits the stage of the 
microscope. The microscope need not be tilted very 
far, and the observer is therefore in a comfortable 
position. The position of the electrometer on the 
stage may readily be changed. All the parts near the 
acid are of hard rubber, thus excluding currents that 
might arise from acid touching metal parts. The 
acid tube is flanged so that the acid cannot creep 
out along the capillary tube. The capillary can 
easily be brought against the wall of the acid tube. 
The tube from which the capillary springs descends 
within the acid tube, thus protecting the capillary 



40 GENERAL PROPERTIES OF LIVING TISSUES 

against breakage. Either tube may at once be re- 
moved from its holder. The platinum wires extend 
to the binding post, and are not simply short pieces 
soldered to copper wire. The wire to the capillary 
tube extends to the bottom of the tube, thus main- 
taining the contact until all the mercury in the tube 
is used. 

About one cubic centimetre of paraffin oil should 
be placed above the piston. Only absolutely clean 
double-distilled mercury should be used. 

As the mercury in the capillary is kept from 
falling by the surface tension, it is obvious that 
whatever increases or diminishes the surface 
tension, for example an electric current, will 
raise or lower in corresponding measure the 
mercury in the capillary. The alteration in sur- 
face tension is accompanied by the movement 
of ions between the meniscus and the remaining 
electrode of the electrometer (the mercury in 
the acid reservoir). In practice it is found that 
this movement can be neither very rapid nor 
long continued, without injuring the sensitiveness 
of the instrument. The potential difference 
from even a single element (Daniell or dry cell) 
is far too large to be used safely. It is advisable 
to employ a potential divider, or rheochord, which 
shall permit only a fraction of the original 
potential (not more than 0.1 volt) to reach the 



METHODS OF ELECTRICAL STIMULATION 41 

electrometer. The platinum should never come 
in contact with the acid. 

The electrometer should be kept short-cir- 
cuited, except during an observation, so that 
the capillary and the mercury in the reservoir 
may always be connected through a conductor. 
The short-circuit key is shown in Fig. 5, B. 
A strip of spring brass connected with one 
of the binding posts of the electrometer rests 
against a second piece of brass connected with 
the other binding post, except when depressed 
by the finger. The point of higher potential, 
when known, should always be connected with 
the capillary. 

When the capillary electrometer is connected 
with two points of unlike potential the meniscus 
is displaced. The pressure' necessary to bring 
it back to its original position is proportional to 
the electromotive force that displaced the me- 
niscus. Thus by connecting the electrometer 
with known differences of potential it may be 
experimentally graduated. In practice, the re- 
lation between the pressure and the potential 
must frequently be redetermined. It is usually 
easier to measure differences of potential, such 
as the demarcation current of nerve or muscle, 
by compensation (Fig. 47, p. 294). In this method 
the electromotive force of the demarcation current 



42 GENERAL PROPERTIES OF LIVING TISSUES 

is measured in fractions of a Daniell cell, or any 
other constant element, by bringing into the same 
circuit with the current of injury, but in an op- 
posite direction, so much of the current from the 
cell as will exactly balance the current of injury, 
i. e. so much as will "keep the meniscus of the 
electrometer from moving in either a positive 
or negative direction when connected with the 
circuit. 

Advantages of the Electrometer. — The mass of 
mercury displaced in the movement of the menis- 
cus is very small, and the distance through which 
it is moved is short. Hence the inertia of posi- 
tion is easily overcome and the inertia of motion 
(which is proportionate to the mass times the 
square of the velocity) is practically wanting. 
The absence of inert'ia errors, the almost instan- 
taneous quickness with which the meniscus takes 
its new position, the ease with which slight elec- 
tromotive forces (-j-q-J-j o" vcut ) ma y be measured, 
and simplicity of construction, are the principal 
advantages of this admirable instrument. 

The Rheochord. — If two poles of a cell or 
other points of different potential be joined by 
a well-drawn wire,, the potential through the 
wire will fall uniformly from the anode to the 
cathode. The greater the resistance in the wire, 
the more uniform will be the fall in potential. 



METHODS OF ELECTRICAL STIMULATION 43 

The Long Rheochord. — In the long rheochord 
(Fig. 6) a metre rule is screwed upon a wood 
base. At each end is a binding post. To post is 
fastened the end of an unbroken German-silver wire 
twenty metres in length. This wire is carried along 
the metre stick to the second post, 1, then wound 
upon a spool, and the end fastened to a third binding 




Fig. 6. The long rheochord ; about one-thirteenth the original size. 

post. The wire upon the metre rule is bare, the 
remaining nineteen metres silk-covered. A conven- 
ient spring contact with binding post slides along the 
metre rule. 

The Square Rheochord. — Upon a block of hard 
maple, 12.5 cm. square, is placed a centimetre scale 
beginning at the 0-post shown on the left side of 
Fig. 7 and ending at the 1 -metre post visible in 
the background to the left. For the sake of clearness 
the numbers on this scale have been omitted from the 
figure. Along the scale, between these two posts, is 
stretched the first metre of a continuous German-silver 
wire, 0.26 mm. in diameter and twenty metres long. 
The remaining nineteen metres of this wire are coiled 
upon a spool, and the free end is fastened to the 
twenty-metre post shown in the background to the 
right of Fig. 7. One of the posts may be turned, in 



44 GENERAL PROPERTIES OF LIVING TISSUES 



order to keep the wire taut, in case changes of tem- 
perature have caused it to lengthen. (This device is 
not shown in Fig. 7.) The under surface of the con- 
tact block is bevelled so that the metal touches the 
wire only with one edge ; the opposite edge is sup- 
ported by a piece of hard rubber. 

A flexible cable leads from the contact block to the 
binding post shown in the foreground to the right. 




Fig. 7. The square rheochord ; two-fifths the actual size. 1 

The resistance in the 20 metres of thin Ger- 
man-silver wire is so great (about 184 ohms) 
that the internal resistance of the element fur- 
nishing the electromotive force, together with the 
resistance of the large copper connecting-wires, 
practically disappears for such measurements as 
we shall need to make. As the fall of potential 
is uniform throughout the 20 metres, the differ- 

1 American Journal of Physiology, 1903, viii, p. xli. 



METHODS OF ELECTKICAL STIMULATION 45 

ence of potential between post and post 1 will 
be practically one-twentieth the electromotive 
force of the element. Thus when the sliding 
contact is at post 1, the capillary electrometer 
receives one-twentieth the electromotive force of 
the element. By moving the slider from post 1 
towards post 0, any desired fraction of this one- 
twentieth may be measured by the electrometer. 

The Simple Key. — A copper bar with hard rubber 
handle is pivoted at one end in a brass post with 
binding screw for electrical 
connection (Fig. 8). ISTear C3 
the other end of the bar is 
a platinum pin, which, 
when the key is closed, 
rests upon a platinum plate 




borne upon a second bind- Fig. 8. The simple key ; about 

three -eighths the actual size. The 
ing post. w i re spring which presses the bar 

The contact bar is held a f inst the ™ ntact plate is not 

shown. 

against the contact plate 

partly by its own weight and partly by a wire spring 
not shown in Fig, 8. When it is desired to break the 
circuit the contact bar is turned back. 

Many experiments in physiology require stimuli of 
uniform intensity. Variations in the make or break of 
the current due to faults in the contacts of the key in 
the primary circuit are a frequent source of error. 
With the key described here the break in tho circuit 
may be made practically uniform. 



46 GENERAL PROPERTIES OF LIVING TISSUES 

The Short-circuiting Key. — Two strips of brass, 
provided with a binding post at each end, are fastened 
to a block of dark slate (Fig. 9). At the centre of 
one strip is a post in which is pivoted a copper bar 
ending in a hard-rubber handle. The bar may be 
lowered between edges of spring brass. 

Polarization. — Connect a platinum and a zinc * 
plate through a simple key with posts and 20 




I" 



v / 



g v o - 



Fig. 9. The short-circuiting key ; 
about three-eighths the actual size. 



Fig. 10. 



of the rheochord as shown in Fig. 10. Connect 
the zero post and the slider with the capillary 
electrometer through a short-circuiting key. 



1 It will be observed that the zinc is amalgamated. Chemi- 
cally pure zinc does not need amalgamation. Commercial zinc 
contains iron, arsenic, etc., as impurities. The contact of una- 
malgamated zinc and these dissimilar metals with an electrolyte 
creates a difference of potential, and parasitic currents run from 
the zinc to the foreign metals. These currents are prevented by 
covering the impurities with zinc amalgam, the electromotive 
properties of which, toward sulphuric acid, are those of pure 
zinc. As the zinc in the amalgam dissolves out, the film of 
mercury unites with fresh zinc. Zinc is amalgamated best by 



METHODS OF ELECTRICAL STIMULATION 47 

Bring the capillary into the field of the micro- 
scope (Leitz objective 3, micrometer ocular), par- 
allel to the micrometer scale. The end of the 
tube should be just visible at the upper margin 
of the field. If the meniscus is not visible, turn 
the pressure screw slowly to the right until the 
meniscus enters the field. Note the position of 
the meniscus on the scale. Close the battery key. 
Let an assistant place the metals in a beaker con- 
taining solution of sodium chloride. Open the 
short-circuiting key of the electrometer. 

When the metals touch the electrolyte a dif- 
ference in potential will be set up, and the 
meniscus will move in the capillary. 

Note the number of divisions of the scale 
traversed by the meniscus. Close the electrom- 
eter key. Wait several minutes. 

Now bring the meniscus back to its original 
position on the scale. Open the electrometer key. 

The meniscus will move to a much slighter 
extent than when the circuit was first made. 

adding 4 per cent of mercury to the molten zinc before casting ; 
or the zinc may be dipped in 10 per cent sulphuric acid to clean 
it, and mercury rubbed over the surface with a brush or a stick 
padded with cloth ; or the zinc may be dipped in a solution 
from which the mercury will deposit on the zinc. Formula for 
amalgamating fluid : warm gently 4 parts mercury in 5 parts 
concentrated nitric acid and 15 parts concentrated hydrochloric 
acid until dissolved, and then add 20 parts more of concentrated 
hydrochloric acid. 



48 GENERAL PROPERTIES OF LIVING TISSUES 

As the displacement of the meniscus is propor- 
tional to the electromotive force of the cell, it is 
obvious that the latter has rapidly diminished. 
The solution contains the ions of water as well 
as those of the salt. When the circuit between 
the platinum and zinc is completed the cations 
H + and Na + move towards the cathode. There 
the more easily de-ionized H + yields up its elec- 
tricity, and hydrogen appears on the cathode. 
The corresponding quantity of electricity is con- 
veyed into the solution at the anode by ioniza- 
tion of the zinc. The deposition of hydrogen 
on the negative plate checks the electromotive 
force setting from the zinc to the platinum in 
two ways : first, because gas is a bad conductor, 
and the effective surface of the platinum is 
thereby diminished by the bubbles collecting 
on it ; and secondly, because hydrogen is electro- 
positive, and creates an electromotive force in 
the direction from platinum to zinc, and thus 
"polarizes" the cell. This new electromotive 
force opposes the original current from zinc to 
platinum. 

The Daniell Cell. — Daniell discovered an elec- 
tro-chemical method of avoiding polarization, and 
thus was able to construct a cell that would 
furnish a current of unvarying strength. In the 
Daniell cell the two metals employed are zinc 



METHODS OF ELECTRICAL STIMULATION 49 

and copper. The amalgamated zinc is placed in 
a porous cup filled with dilute sulphuric acid. 
The copper is placed in a solution of copper sul- 
phate kept saturated by crystals of the salt, 
When the circuit is closed, the zinc "dissolves" 
in the sulphuric acid, carrying with it the elec- 
tricity with which the zinc ions are charged. 
The electricity is carried through the solution 
by the migration first of hydrogen and then of 





Fig. 11 A. 

A, earlier form of pole-changer. The rubber handle prevents the cross, 
ing of the current from one side cup to the other. B, diagram of pole- 
changer arranged (1) to change the direction of the current, (2) as a double 
key, without cross-wires, (3) as a simple key. 

copper ions. It leaves the solution at the cath- 
ode where the copper ions are converted into 
metallic copper and deposited on the cathode. 
The quantity of zinc dissolved and copper de- 
posited is proportional to the quantity of the 
current. One ampere deposits per minute 19.75 
milligrams copper, and dissolves 20.32 milligrams 

zinc. 

4 



50 GENERAL PROPERTIES OF LIVING TISSUES 

It is to be observed that each metal is placed 
in a solution of its own salt. The ions carried to 
the respective poles are of the same nature 
chemically as the poles themselves, and hence do 
not set up opposing electromotive forces when 
they are de-ionized. 

The current produced by the Daniell cell is 
almost perfectly constant, so long as sulphuric 
acid still remains uncombined, and so long as 
the sulphate of copper solution is kept saturated. 




Fig. 12. Rocking key, metal contact ; about one-half the actual size. 

It may be remarked that the function of the 
porous cup is to keep the copper from depositing 
on the zinc. 



The Pole-Changer. 1 — The instrument illustrated 
by Fig. 12 serves as a simple key, short-circuitiug 
key, and pole-changer. No mercury is used. 

1 Science, 1905, xxi, pp. 752-754. 



METHODS OF ELECTRICAL STIMULATION 51 

The central binding posts are prolonged upwards 
and each is slotted to receive a brass bar, which is 
pivoted in the slot by a horizontal pin. The brass 
bars are held parallel by two rubber rods which serve 
as handles. When the bars are depressed to one side 
or the other, they engage between plates of spring 
brass set into brass blocks, each of which carries a 
binding screw. Cross-wires enter these blocks, as 
shown in the figure. At one end the cross- wires are 
soldered into the blocks, thus making an electrical 
contact. The two blocks at the other end are per- 
forated by rubber cores or " bushings " through which 
the cross-wires pass. The cross-wires, therefore, make 
no electrical contact with these blocks. When a con- 
tact is desired, the nut borne on the head of each 
cross-wire is turned until its face presses against the 
brass block outside the bushing. In this position the 
key serves as a pole-changer, or commutator. When the 
nut on the cross-bar between the central posts is turned 
until its face presses against the post, it will short- 
circuit the central posts. 

Polarization Current. — Place two pieces of 
platinum foil in a solution of copper sulphate, 
and connect them to a pole-changer (without 
cross-wires). Connect the remaining pairs of 
posts with two dry cells in series (carbon of one 
cell connected with zinc of other), and with the 



52 GENERAL PROPERTIES OF LIVING TISSUES 




and 1 metre posts of the rheochord, respectively. 
Connect the zero post and the slider to the capil- 
lary electrometer (Fig. 13). Turn the pole- 
changer to pass the battery current through the 
copper sulphate solution or " electrolyte." The 

cation (copper) will be 
partially de-ionized at 
the negative pole, or 
cathode, on which cop- 
per will be deposited 
in a fine film. The anion 
(sulphion, S0 4 ) will pass 
towards the positive pole, 
or anode, where it gives 
up its electric charge and 
becomes the ordinary radical S0 4 . This radical 
cannot exist uncombined in water, but forms sul- 
phuric acid, setting free oxygen, which therefore 
appears at the anode. 

The elements copper and oxygen deposited 
respectively on the cathode and anode tend to 
fly back into the ionic state ; and this ten- 
dency, taken in connection with the opposing 
osmotic force of the ions already in solution, 
sets up an electromotive force equal to that 
which caused the de-ionization, but in an op- 
posite direction. Hence the polarization cur- 



Fig. 13. 



METHODS OF ELECTRICAL STIMULATION 53 

rent. On cutting off the electrolyzing current, 
the polarization current may be measured. 

Note the position of the meniscus of the capil- 
lary electrometer. Turn the pole-changer so that 
the cell is cut off and the electrodes are brought 
into the electrometer circuit. 

The meniscus will indicate a current opposite 
in direction to the current from the cell. 

Dry Cell. — A " dry " cell is very convenient 
for large classes. It usually consists of a zinc 
cup, lined with plaster of Paris, saturated with 
ammonium chloride, in the centre of which is a 
carbon plate surrounded with black oxide of 
manganese. When the cell is in action, the zinc 
forms a double chloride of zinc and ammonium 
while ammonia gas and hydrogen are liberated 
at the carbon pole. These cells should never be 
used continuously for many minutes, for they are 
rapidly polarized by the accumulation of hydro- 
gen on the carbon plate. The unused cell re- 
gains its difference of potential by the union of 
the hydrogen with the oxygen slowly given off 
by the manganese dioxide, which therefore acts 
as a depolarizer. 

Induction Currents 

A most useful method of electrical stimulation 
of living tissues is by the induced current, and 



54 GENERAL PROPERTIES OF LIVING TISSUES 

a clear idea of the phenomena of induction must 
now be gained. 

The Inductorium 1 — The primary coil of the in- 
ductorium (Fig. 14), wound with double silk-covered 
wire of 0.82 mm. diameter, having a resistance of 0.5 




Fig. 14. The inductorium ; one-third the actual size. (The set screw 
holding the trunnion block tube against the side rod is not shown.) 



ohm, is supported in a head-piece bearing three bind- 
ing posts and an automatic interrupter. The core 
consists of about ninety pieces of shellacked soft 
iron wire. This core actuates the automatic inter- 
rupter. The interrupter spring ends below in a collar 
with a set screw. By loosening the screw, the inter- 
rupter with its armature may be moved nearer to or 



1 American Journal of Physiology, 1903, p. xxxv. 



METHODS OF ELECTRICAL STIMULATION 55 

farther from the magnetic core. Once set, the inter- 
rupter will begin to vibrate as soon as the primary 
circuit is made. The outer binding posts are used for 
the tetanizing current. The left-hand outer post and 
the middle post are used when single induction cur- 
rents are desired ; they connect directly with the ends 
of the primary wire, thus excluding the interrupter. 
These several connections upon the head-piece are 
simply arranged and are all in view ; there are no con- 
cealed wires. 

From the head-piece extend two parallel rods 22 
cm. in length, between which slides the secondary coil, 
containing 5000 turns of silk-covered wire 0.2 mm. in 
diameter. Over each layer of wire upon the secondary 
spool is placed a sheet of insulating paper. Each end 
of the secondary wire is fastened to a brass bar 
screwed to the ends of the hard-rubber spool. 

The brass bars bear a trunnion which revolves in 
a split brass block, the friction of which is regulated 
by a screw. The trunnion block is cast in one piece 
with a tube 3 cm. in length, which slides upon the 
side rods. A set screw, not shown in Fig. 14, holds 
the trunnion block tube and the secondary spool at 
any desired point upon the side rods. This screw 
also serves to make the electrical contact between the 
trunnion block tube and the side rod more perfect. 
The secondary spool revolves between the side rods 
in a vertical plane. When the secondary coil has 
revolved through 90°, a pin upon the side bar of 
the secondary coil strikes against the trunnion block 



56 GENERAL PROPERTIES OF LIVING TISSUES 

and prevents further movement in that direction. 
The right-hand side bar bears a half-circle graduated 
upon one side from 0° to 90°. An index pointer is 
fastened upon the trunnion block. One side rod is 
graduated in centimetres. 

The side rods end in the secondary binding posts, 
so that moving the secondary coil does not drag the 
electrodes. Next the binding posts is placed a short- 
circuiting key. 

Magnetic Induction. — Faraday's experiment. 
Eemove the secondary (larger) coil of the in- 
ductoriuni (Fig. 14) from its slideway and con- 
nect its terminals with the capillary electrometer. 
Eaise the brass bridge between the binding posts. 
(If this bridge is down its thick metallic mass 
will offer such an easy path between the ends of 
the secondary wire that nearly all — practically 
all — the electricity produced in this coil will 
pass over the bridge, instead of by the relatively 
long, thin wires leading to the electrometer.) 
Bring the meniscus into the field. Thrust 
the north pole of a magnetized rod within the 
coil. 

The meniscus will move, indicating that an 
electric current has been induced in the second- 
ary coil. Note the direction of the current. 

Let the magnet remain in the coil. 

The meniscus will return to its former position. 



METHODS OF ELECTRICAL STIMULATION 57 

Evidently the induced current is of momentary 
duration. 

Withdraw the magnet quickly. 

The meniscus will move in the opposite 
direction. 

Insert the south pole. 

The induced current now has the direction 
opposite to that of the current induced by the 
insertion of the north pole. 

Withdraw the magnet quickly. 

The induced current has the direction opposite 
to that of the current induced by the withdrawal 
of the north pole. 

These results may be thus expressed : the 
moving of a magnet in the neighborhood of a 
conductor, or of a conductor in the neighbor- 
hood of a magnet, produces in the conductor an 
electromotive force, which, on the circuit being 
completed, creates a current that would impart 
to the magnet or the conductor a movement in 
the opposite direction. 

Magnetic Field. Lines of Force. — The space 
about a magnet in which the magnetic forces 
act is called the " field " of the magnet. If very 
fine iron filings are dusted through a muslin 
cloth onto a thin card perforated near the centre 
by a copper wire or other conductor, and a strong 
current is passed through the wire, the filings will 



58 GENERAL PROPERTIES OF LIVING TISSUES 

arrange themselves in concentric circles around 
the wire, particularly if the card be gently 
tapped. 

The position of these "lines of force" shows 
the direction of the magnetic force, and their 
number is an index of its intensity. 

To produce Electric Induction, the Lines of 
Magnetic Force must be cut by the Circuit. — 
Hold the magnet at right angles to the axis of 
the coil, and, keeping it in this position, rapidly 
advance it towards the coil. 

The electrometer will show no current, because 
the number of the lines of magnetic force which 
pass through the field of the conductor has not 
been altered. 

Electro-magnetic Induction. — An electro-magnet 
may be used in place of the bar magnet to pro- 
duce induction. 

Connect a dry cell through a simple key with 
posts 1 and 2 of the primary coil. 1 Close the 
key. 

When the current passes through the primary 
coil, the core of iron wire in the coil will be 

1 It will be convenient to use the numbers 1 and 2 to desig- 
nate the posts connected directly with the ends of the primary 
wire, excluding the vibrating hammer ; the numbers 2 and 3 
will indicate the posts that connect with the ends of the pri- 
mary wire including the hammer. When the battery is con- 
nected with posts 2 and 3 the hammer will vibrate. 



METHODS OF ELECTRICAL STIMULATION 59 

magnetized, as is shown by its attracting the 
head of the Wagner hammer. 

Bring the meniscus into the field. Approach the 
primary coil to the secondary as in the experiment 
with the magnet. Withdraw the primary coil. 

The electrometer shows the presence of in- 
duced currents, as before. These currents are 
momentary. The first induction current is in- 
verse, i. e. it runs round the secondary coil in the 
direction opposite to that taken by the battery cur- 
rent in the primary coil. The second induced cur- 
rent is in the same direction as the primary current. 

Place the coils at right angles to each other. 
Approach one towards the other. 

No current will be induced. 

Make and break Induction. — Close and open 
the key in the primary circuit, thus making and 
breaking the primary current. 

The effect is the same as if the primary were 
suddenly brought up to the secondary coil from 
an infinite distance and removed again. The make 
induction current is in the opposite, the break in 
the same, direction as the primary current. 

Turn the secondary coil on its pivot until the 
axis is at right angles to the axis of the primary 
coil. Make and break the primary current. 

No induction will take place provided the 
angle between the coils is precisely 90°. 



60 GENERAL PROPERTIES OF LIVING TISSUES 

On the Construction of the Inductorium. — Ex- 
amine the construction of the inductorium. The 
primary coil consists of a few turns of thick wire. 
More turns would increase resistance and self- 
induction, — the counter induction set up in each 
turn of the primary wire by the passage of the 
primary current through neighboring turns, — 
without increasing the induction effect in the 
secondary coil. 

The iron core adds to the number of lines of 
magnetic induction which pass through the coils. 
It has been already shown (page 58) that the 
lines of magnetic induction produced by the pas- 
sage of an electric current through a wire are 
closed circles. If the centre of the coil were 
filled with air, most of these circles would remain 
closed about their own wire, for air is not readily 
permeable to magnetism. But when the iron core 
is placed within the coil the greater part of the 
magnetic induction follows the iron (because it 
is more permeable) from end to end of the core, 
returning outside through the air. Thus the 
number of effective lines is increased. A bundle 
of iron wires is used instead of a solid core, be- 
cause no induced current is then possible through 
the mass of the iron, as would be the case in a 
solid core. Such a current would slow the speed 
of magnetization and demagnetization. 



METHODS OF ELECTRICAL STIMULATION 61 

The secondary coil is made of many turns of 
fine wire, because the object of the inductorium 
is to transform the low electromotive force of the 
cell into the high electromotive force of the in- 
duced current. In the induction coil, as in other 
transformers, the electromotive forces in the 
primary circuit are to those produced in the 
secondary circuit approximately as the number 
of turns of wire in the primary is to the number 
in the secondary circuit. 

If the induced current is to be passed through 
conductors of low resistance, the high internal 
resistance of the secondary coil, due to its great 
length of fine wire, will be of importance. 

Place a dry cell with simple key in the pri- 
mary circuit of an inductorium (posts 1 and 2). 
Connect the secondary coil with a galvanometer. 
Note the excursion of the needle with a break 
induction current. Eeplace the secondary coil 
with one of fewer windings (the primary coil of 
a second inductorium will serve). Let the dis- 
tance between primary and secondary coil be the 
same as before. 

The excursion of the needle with a break in- 
duction current will be increased, or at least not 
proportionately diminished. 

If, on the other hand, the induced current is 
to be passed through nerve, muscle, or skin, the 



62 GENERAL PROPERTIES OF LIVING TISSUES 

resistance of the secondary coil will practically 
be nothing in comparison with the enormous 
resistance of animal tissue. 

Eepeat the preceding experiment, introducing 
in the secondary circuit a high external resist- 
ance, i. e. a nerve. 

The secondary coil with many turns of fine wire 
now causes a much greater deflection of the gal- 
vanometer needle than the coil with fewer turns. 

Interrupter. — Instead of making and break- 
ing the primary circuit by hand, an automatic 
interrupter is provided. The primary circuit 
passes through a screw, the point of which con- 
veys the current through a flat spring upon 
which is mounted an iron disk opposite and near 
to the core of wire in the primary coil. When 
the current enters the primary coil, the core is 
magnetized and draws upon the iron disk. The 
spring, to which the disk is attached, is thereby 
drawn away from the screw-point through which 
the current is passing. Thus the current is 
broken, and ceases to flow through the primary 
coil ; the core no longer is magnetized, and re- 
leases the iron disk ; the spring again makes 
contact with the screw-point, the current is re- 
established, only to be at once again broken. 
Thus a rapid series of make and break induc- 
tion currents is secured. 



METHODS OF ELECTRICAL STIMULATION 63 

Draw a diagram of the primary circuit, indi- 
cating the connections of the inductorium. 

Empirical Graduation of Inductorium. — Con- 
nect the secondary coil with the galvanometer. 
Join the primary coil to a dry cell, interposing a 
simple key. Turn the secondary coil on its pivot 
until it is at right angles with the primary coil. 
Close the circuit. 

The galvanometer needle will not swing. 
There is no induced current. 1 

Turn the secondary coil on its pivot, closing 
the key from time to time to test the induction. 

The strength of the induction increases ap- 
proximately as the cosine of the angle between 
the coils increases. An empirical graduation is 
sometimes placed on a circular scale beneath the 
coil. 

When the axes of the two coils lie in the same 
plane, slide the secondary towards the primary, 
making and breaking the primary current from 
time to time. 

The potential of the primary upon the second- 
ary coil, i. e. the sum of the inductions of each 
element of the primary upon all the elements of 
the secondary coil, increases as the secondary is 
brought nearer the primary coil. The increase is 
not linear. As the distance between the coils 

1 It is difficult to place the coil precisely at an angle of 90.° 



64 GENERAL PROPERTIES OF LIVING TISSUES 

diminishes, the increment of increase in the in- 
tensity of the induced current is not the same 
but greater for each centimetre of approach. 

Graduation. — Fasten a strip of white gummed 
paper at the side of the base of the inductorium, 
beginning at the end block which holds the 
primary coil. Place the secondary coil at the 
end of the slideway. Make the primary current. 
Read the number of degrees of deviation for the 
break induction current only. Make a line on 
the paper band exactly opposite that end of the 
secondary coil which is nearer the primary. 
When the needle is again at rest, move the 
secondary nearer the primary coil, and find the 
distance at which the deviation of the needle in 
response to the break induction current is n de- 
grees (for example, two) of the scale larger than at 
the former position of the coil. Mark on the white 
strip the new position of the coil. Continue in 
this way to find the positions of the secondary 
coil at which the needle shows successively a 
deviation two degrees greater at each new posi- 
tion, and mark them on the paper band. 

The marks on this empirical scale will be 
nearer together as the secondary approaches the 
primary coil. 1 

1 The rough method here employed serves merely to show- 
that the increase in the intensity of the induction current as 



METHODS OF ELECTEICAL STIMULATION 



65 



The Platinum Electrodes. — The stimulating elec- 
trodes are provided with platinum points projecting 
about 10 mm., polished hard-rubber handle, 7.5 cm. 
long, and very flexible silk-covered connecting wires 
65 cm. long, ending in nickel-plated brass tips (Fig. 
15). The rubber handle is in two pieces, screwed 
together, permitting easy access to the connection 
between the flexible wire and the 
stiff wire into which the platinum 
points are inserted. 

The Flat-jawed Clamp. — The 
flat-jawed clamp, or " Femur 
Clamp" (Fig. 16), consists of 
strong, smoothly working brass 
jaws attached to a steel rod. 
The jaws are separated by a spring 
and brought together by a screw. 
They will hold objects of widely 
varying size, -for example, the t^g*- 4 "* 
femur of a nerve-muscle prepara- 
tion or a board a centimetre thick. The clamp has a 
binding post for making electrical connection with a 
muscle or other conductor held between its jaws. 

The Round-jawed Clamp. — The round-jawed clamp 
is convenient for holding burettes, tubing, rods, ther- 
mometers, etc. (Fig. 16). 

The Double Clamp. — This is a strong clamp of 
enamelled iron with two brass nickelled screws (Fig. 

the coils approach is not linear. An exact method of gradua- 
tion has been given by Kronecker. 

5 




Fig. 15. 



66 GENERAL PROPERTIES OF LIVING TISSUES 

17). The screws move into an angle, against the sides 
of which a large or small rod may be held firmly and 
without sidelash. 

Make and Break Induction Currents as Stimuli. 
— Make a nerve-muscle preparation. Connect a 
dry cell with simple key to the primary coil 
(posts 1 and 2). Fasten in the posts of the 




Fig. 16. The flat-jawed clamp and the round-jawed clamp ; one-fourth 
the actual size. 



secondary coil the stimulation electrodes, i. e. 

the prolongation of the ends of the secondary 

wire which convenience demands. Put the 

secondary coil at the end of the slideway and 

turn the coil. Place the 

^it-^EJv^v electrode points against 

tH^^^^^O*! the nerve. Open and close 

the primary circuit. 

Tig. 17. The double clamp, one- ml , ■, . 

third the actual size. The muscle does not 

contract. 
Move the secondary towards the primary coil, 
opening and closing the primary circuit. 



METHODS OF ELECTRICAL STIMULATION 67 

Presently the muscle will shorten. (Compare 
pages 175 and 176.) Observe that this contrac- 
tion was the result of a break induction current, 
not a make. 

Cautiously move the secondary coil still nearer 
the primary, making and breaking the current as 
before. 

A point will be reached at which the make 
induction also causes contraction. Obviously, 
the break current is a stronger stimulus than 
the make induction current. The cause of the 
greater intensity of the break induction current 
lies in the primary coil. The current which en- 
ters the primary coil induces a current in this 
coil as well as in the secondary coil. The direc- 
tion of this "self -induced" current is opposite to 
that of the primary current, and hence weakens 
it and delays its development. The stimulating 
power of electricity increases with both the inten- 
sity of the current and the quickness with which 
the intensity alters. Hence the stimulating power 
of the make induction current is lessened by the 
self-induction of the primary coil. When, on 
the other hand, the primary circuit is broken, 
the current stops, and although self-induction 
again takes place, it cannot affect the primary 
current, because the latter no longer exists. The 
self-induced current at the break of the primary 



2 



t 



68 GENERAL PROPERTIES OF LIVING TISSUES 

current is in the same direction as the primary 
current before the break. 

The Extra Currents at the Opening and Closing 
of the Primary Current. — 1. Remove the secon- 
dary coil from the inductorium. Connect posts 
1 and 2 of the primary coil with a dry cell, inter- 
posing a simple key. Fasten the ends of the 
electrode wires in these same 
posts. Close the primary cir- 
cuit. Place the electrode 
points against the tongue. 
Open the key. 

A shock from the self- 
induced current developed in 
the primary coil will be felt. 
Fig. is. Draw a diagram of the circuits. 

2. Connect a dry cell through 
a key to the metre posts of the rheochord (Fig. 
18). Connect the positive post and the slider to 
the primary coil of an inductorium arranged for 
single induction currents. Bring wires from these 
posts of the primary coil through a simple key 
to the nerve of a nerve-muscle preparation. Close 
the key in the primary circuit. Open and close 
the key in the nerve circuit. The muscle will 
contract at closure and possibly at opening. By 
means of the slider, weaken the current through 
the primary coil until opening and closing the 




°\^K 



METHODS OF ELECTRICAL STIMULATION 69 

key to the nerve no longer produces contraction. 
Now let this key remain closed and make and 
break the primary circuit. 

The muscle will contract both on opening and 
closure. The induction currents developed in 
the primary coil when the primary current is 
made and broken stimulate the nerve, al- 
though the galvanic current itself is powerless 
to do so. 

Tetanizing Currents. — Connect a dry cell to 
posts 2 and 3 of the primary coil. The vibrat- 
ing hammer will automatically make and break 
the current. Place the electrodes against the 
nerve or muscle. 

The muscle will contract once for each induc- 
tion current, but the contractions are so rapid 
that they fuse into a prolonged shortening termed 
tetanus. 

Induction in Nerves. — Faraday discovered that 
currents can be induced in electrolytes as well 
as in metallic conductors. Induced currents may 
therefore appear in nerves lying sufficiently near 
a primary circuit. 

Lay the well-moistened nerve of a nerve-muscle 
preparation around the primary coil protected by 
a piece of paraffin paper in such a way that the 
free end of the nerve touches the nerve near the 
muscle or touches the muscle itself, so as to form 



70 GENERAL PROPERTIES OF LIVING TISSUES 

a closed circuit. Make and break the primary 
current. 

Make and break currents will be induced in 
the nerve, and the muscle will contract. 

Exclusion of Make or Break Current. — Con- 
nect the dry cell with posts 1 and 2, interposing 
a key. See that the short-circuiting key, i. e. the 
thick brass bridge between the posts on the sec- 
ondary coil, is down. Connect the electrodes 
with the secondary coil, and place their points 
against the nerve of a nerve-muscle preparation. 
Close the primary key. 

The muscle will not contract. 

The resistance to the passage of the induced 
current through the portion of nerve between 
the ends of the electrodes is many thousand 
times greater than the resistance of the brass 
bridge or short-circuiting key. Practically none 
of the electricity will pass through the nerve 
when the short-circuiting key is closed. 

Open the short-circuiting key and then open 
the primary key. 

The muscle contracts. 

Eepeat the experiment, letting the make cur- 
rent pass and short-circuiting the break. 

With the primary key and a short-circuiting 
key either break or make induced currents can 
be used as stimuli at will. 



methods of electrical stimulation 71 

Unipolar Induction 

1. Arrange the inductorium for tetanizing 
currents (posts 2 and 3). Make a nerve-muscle 
preparation. Lay it on a clean dry glass plate. 
Let the nerve rest on a wire connected with one 
pole of the secondary coil. Set the inductorium 
in action. Connect the muscle with the earth 
by touching the muscle with the end of a wire 
the other end of which rests on a gas or water 
pipe. 

The muscle will show tetanic contractions, 
provided the induced current is sufficiently 
strong. If no tetanus is seen, move the second- 
ary coil completely over the primary. 

Unipolar induction may be produced by the 
electric currents in the skin. This may be 
demonstrated with a sensitive nerve-muscle prep- 
aration. 

2. Ligature the nerve between the electrode 
and the muscle, and repeat the experiment. 

Stimulation will still be secured. The uni- 
polar discharge passes through the entire length 
of nerve and muscle to or from the point at 
which the connection with the earth is made, and 
thus stimulates the entire preparation. 

DuBois-Reymond, who was the first to make 
the preceding experiments, pointed out that 



72 GENERAL PROPERTIES OF LIVING TISSUES 

whenever the secondary circuit was open (i. e. 
when the bridge between the ends of the second- 
ary wire was up) the making and breaking of 
the primary circuit caused free electricity to 
gather on the ends of the secondary wire. When 
the electro-static induction becomes great enough 
the electromotive force overcomes the resistance 
in whatever connecting path may be offered, and 
the electricity passes from the coil to the earth. 
If a part of the path is formed by irritable 
tissues, they will of course be stimulated. 

3. The quantity of electricity passing through 
the nerve may be increased by approximating 
the coils or by increasing the electrical capacity 
of the conductor, as follows : — 

Eemove the wire connecting the preparation 
with the gas pipe. Set the inductorium in action. 
Touch the muscle with the moistened finger. 

Contraction follows. 

Here the electrical capacity of the preparation 
is increased by connecting the preparation with 
the human body, a conductor of large surface 
(and through it with the earth). A similar 
result is obtained by unipolar stimulation of 
nerves and muscles while still in the body of 
the animal, as in many physiological experi- 
ments. It is not necessary that the surface of 
the conductor be enormously large. The follow- 



METHODS OF ELECTRICAL STIMULATION 73 

ing experiment shows that even very small sur- 
faces will suffice. 

4. On a carefully dried, clean glass plate lay 
four nerve-muscle preparations. Let the nerve 
of the first rest on a single wire the other end of 
which is fastened in one of the binding posts of 
the secondary coil. Place the end of the second 
nerve on the tendon of the muscle of the first 
preparation, the third on the second tendon, and 
the fourth nerve on the tendon of the third. 
Remove the secondary coil some distance (a few 
centimetres) from the primary, and set the in- 
ductorium in action. Gradually approximate 
the coils. 

As the tension at the ends of the secondary 
wire increases by the approximation of the coils, 
the first preparation will contract. On further 
approximation, the first and second; then the 
first, second, and third ; and finally all four will 
contract. 

This instructive experiment shows that when 
the conducting surface is small, as in the present 
instance, the unipolar action is greater on the 
parts nearer the secondary wire than on parts 
farther away. The danger of unipolar action on 
tissues lying near the electrodes in ordinary 
artificial stimulation of nerves and muscles in 
situ is obvious. 



74 GENERAL PROPERTIES OF LIVING TISSUES 

5. It is not even necessary that the conductor 
should be actually in contact with the prep- 
aration. 

Connect a nerve-muscle preparation, insulated 
on a glass plate, with one pole of the secondary 
coil, and set the inductoriurn in action. The 
secondary coil should completely cover the pri- 
mary. Bring a moistened linger as near the 
muscle as possible without touching it. 

With the proper intensity of the primary cur- 
rent, contraction will take place, though absent 
when the finger is removed. 

The sudden approach of a condenser charged 
with static electricity will stimulate an isolated 
nerve or muscle. 

6. The danger of error from unipolar action is 
particularly great in electrometer observations on 
the current of rest or action current of nerve and 
muscle, discussed and demonstrated experiment- 
ally in Part III, Chapter II. 

The errors due to unipolar action can usually 
be prevented by the following precautions : The 
secondary coil should always be connected with 
the tissue to be stimulated through a short- 
circuiting key, which should be kept closed ex- 
cept during the intentional stimulation of the 
tissue. With this good metallic connection be- 
tween the ends of the secondary wire there will 



METHODS OF ELECTRICAL STIMULATION 75 

be no static electrification. Further, the appear- 
ance of positive and negative electricity during 
the period of stimulation must be provided 
against, especially if that period is at all pro- 
tracted, for it must not be forgotten that the 
bridge of nerve, which completes the secondary 
circuit by uniting the two electrodes, possesses 
very higli resistance, and thus affords but an 
imperfect closure of the ends of the secondary 
wire. This provision is made by connecting the 
positive electrode with the earth by a good con- 
ductor, for example by a copper wire leading 
from the electrode to the gas or water pipe 
In case of doubt, a control experiment should 
be made. The nerve should be severed between 
the stimulated point and the muscle, and one 
end laid on the other. Excitation through the 
passage of a nerve impulse along the nerve is 
thereby made impossible. If the muscle still 
contracts when the nerve is stimulated above 
the section, it is because of unipolar stimulation. 

An additional reason for care is that the insu- 
lation of the secondary spiral is injured by leav- 
ing the secondary circuit open while the hammer 
of the inductorium is in action. 

It may be stated that the direction of the uni- 
polar discharge is of importance. Excitation 
takes place only where the positive charge enters 



76 GENERAL PROPERTIES OF LIVING TISSUES 

the nerve or the negative charge leaves the 
nerve. 

The break induction current is more effective 
than the make, as the slower development of the 
latter causes the terminals of the secondary wire 
to be charged more slowly than by the rapidly 
developed break current. 

Apparatus. 

Normal saline. Bowl. Towel. Pipette. Glass plate. 
Zinc wire, 4 inches long. Copper wire, 4 inches long. Por- 
celain dish. Mercury. 5 per cent sulphuric acid. 5 per 
cent solution of potassium chromate. Iron wire, 4 inches 
long. Musele clamp. Iron stand. Capillary electrometer. 
Rheochord. Microscope (micrometer ocular, objective 3). 
Daniell cell. Dry cell. Two platinum electrodes. Ziuc 
electrode. Beaker. Sodium chloride. Simple key. 9 
wires, 2 feet long. Saturated solution of copper sulphate. 
Pole-changer (in paper dish). Inductorium (with elec- 
trodes). Coil with few windings (primary coil of a 
second inductorium). Bar magnet. Iron filings. Galva- 
nometer. Card, with thick copper wire. Ligatures. 
Frogs. Osmometer (for demonstration). Tradescantia 
discolor. Serum. Sodium chloride solutions (0.60, 0.65, 
0.70, 0.75, 0.80 and 5.0 per cent, also 0.62, 0.61, 0.60, 
0.59, 0.58, and 0.57 per cent). Microscope. Defibrinated 
blood. Twelve test-tubes. Tension indicator. Soap solu- 
tion. Lycopodium. Alcohol. 



THE GRAPHIC METHOD 77 



III 

THE GRAPHIC METHOD 

The studies next to be undertaken make use of 
the change of form of the contracting muscle as 
a partial index to the transformation of energy 
in the tissue. A permanent record is desirable. 
Further, the changes in the dimensions of the 
muscle are so small that it is necessary to have 
the graphic record enlarged, rather than of actual 
size. To satisfy these conditions, the muscle is 
attached near the fulcrum of a lever furnished 
with a recording point. The surface for the 
writing is usually glazed paper which has been 
covered with a thin layer of soot by passing the 
paper through the luminous part of a broad gas 
flame. The paper is fastened (before smoking) 
on a plate or on a drum which moves past the 
writing point, almost parallel to it, and furnishes 
thus a continuously fresh surface. 1 

1 The paper is cut wider and longer than the surface of the 
drum. The extra width is to protect the bearings of the drum 
from soot that might otherwise collect there in smoking the 



78 GENERAL PROPERTIES OF LIVING TISSUES 

The writing point rubs off the soot in its path 
and leaves a white magnified tracing of the 
muscle's change in length or whatever dimen- 
sion is the subject of record. The paper is then 
removed, drawn through a saturated solution of 

paper. The extra length allows the edge of the overlap to be 
gummed to the paper below, permits the paper to be removed 
from the drum by cutting through the overlap parallel to the 
mucilage, — the surface of the drum being protected from the 
knife by the underlying paper, — and provides an unsmoked 
surface by which the paper can be handled on its removal from 
the drum. The drum should be laid in the centre of the strip 
of paper, the gummed edge to the left, and the axis of the drum 
precisely at right angles to the long axis of the paper ; the 
mucilage should be moistened, and the ends of the paper 
brought around and fastened. If the paper is awry, the sur- 
face will not lie uniformly against the drum and the record 
will be deformed. The drum should now be placed in the 
smoking apparatus, revolved uniformly and not too fast, 
brought over the gas flame, lowered just below the upper edge 
of the flame, and covered with a chocolate brown layer of soot, 
beginning at the operator's left hand and passing gradually to 
the right. The speed should be such that one passage from 
left to right shall suffice. To trim the edges, hold the drum 
in the left hand, inclined downwards, and pass a sharp knife- 
blade around the lower edge. The handle of the knife should 
be kept lower than the blade, to avoid tearing. In removing 
the paper from the drum, hold the drum in the air with the 
left thumb pressed on the edge of the paper near the overlap, 
and cut through the overlapping edge near the mucilage. The 
loosened paper will hang down and may then be seized by the 
unsmoked overlap. In recording, let all the curves begin near 
the overlap. Attention to these details is indispensable to the 
best technical results. 



THE GRAPHIC METHOD 79 

white shellac in 95 per cent alcohol, 1 and hung 
up until the alcohol is evaporated. The soot 
will thus be coated over and held in place by 
a thin layer of shellac, and the record will be 
secure. 

The Kymograph. — The improved kymograph 2 
is shown at the right of Fig. 19, in which it is mounted 
as part of the long paper device. It consists of a 
drum revolved by clockwork and also arranged to be 
more rapidly revolved or " spun " by hand. 

The drum is of aluminium, cast in one piece 
turned true in the lathe to a circumference of 50 cm. 
The height is 15.5 cm. The weight is about 600 
grams. The drum slides upon a brass sleeve in bear- 
ings 1.1 cm. deep (to prevent " sidelash"), and is 
held at any desired height by a spring clip. The 
sleeve ends in a friction plate, which rests upon a 
metal disk driven by the clockwork. Sleeve and 
friction plate revolve about a steel shaft which passes 
through both the heavy plates containing the clock- 
work, and is securely bolted to the bottom plate. 
The sleeve bears upon the steel shaft only by means 
of " bushings " at the ends of the sleeve, thus securing 

1 To make this solution, the alcohol should be allowed to 
stand on the shellac a month or more before using. A satisfac- 
tory solution may be made in twenty-four hours by dissolving 
375 grams of rosin in 2500 c.c. of alcohol. 

2 Introduction to Physiology, 1901, p. 51. American Jour- 
nal of Physiology, 1903, viii, p. xxxvii. Ibid., 1904, x, p. 
xxxix. Science, 1906. 



80 GENERAL PROPERTIES OF LIVING TISSUES 

a bearing without " sidelash " and with little friction. 
As the sleeve with the drum rests upon the friction 
plate by gravity alone, it is easy to turn the drum by 
hand either forward or back, even while the clock- 
work is in action. At the top of the sleeve is a screw 
ending in a point which, when the screw is down, 
bears upon the end of the steel shaft and lifts the 
sleeve, and with it the drum, until the sleeve no 
longer bears upon the friction plate. The drum may 
then be " spun " by hand about the steel shaft. The 
impulse given by the hand will cause the drum to 
revolve for about one minute. The speed during any 
one revolution is practically uniform. 

The clockwork consists of a stout spring about 
6 metres in length, driving a chain of gears. The 
speed is mainly determined by a fan slipped upon an 
extension of the last pinion shaft in the chain. Four 
fans of different sizes are provided. 

The speed is regulated by a governor on the shaft 
that carries the fan. When the milled head shown to 
the right of the steel shaft in Fig. 19 is up, the gear 
on the extreme right of the chain no longer engages 
with the gear driven by the spring, but runs " idle," 
while the gear attached to the friction plate engages 
with the lower of the two gears at the left ; the pinion 
of this lower left-hand gear engages with the spring 
gear. Fast speeds are then obtained. 

When the milled head is down, the gear attached 
to the friction plate falls below the left-hand gear, 
while the right-hand gear engages with the spring 



THE GRAPHIC METHOD 81 

gear and through a pinion drives the friction-plate 
gear. Slow speeds are then obtained. 

These operations are easily and rapidly performed, 
though, as in all gear mechanism, an instant's pause 
is sometimes required to enable the gear teeth to 
engage. The clockwork should be in motion, without 
the fan, when the adjustments are being made. 

With both fast and slow gearing four fans of 
different areas may be used. They are slipped upon 
an extension of the last pinion shaft in the chain. 
Five slow and five fast speeds (exclusive of spinning) 
are thus obtained. An additional slow speed (50 cm. 
per hour) may be obtained with a very large fan. 
All speeds are regulated by a friction governor fast- 
ened to the same shaft that carries the fan. With 
one winding the drum will revolve from about one 
to about seven hours, or longer, depending on the 
fan employed. 

The Long Paper Kymograph. 1 — In Fig. 19 the 
kymograph is arranged for use with a sheet of smoked 
paper about eight feet long. A rigid bench of steel 
about 97 centimetres long firmly supports two 
]]-shaped castings in which two aluminium drums 
revolve on pointed adjustable bearings. One of the 
castings slides along the bench, and may be fastened 
at any desired distance from the remaining or clock- 
work drum, so that paper from about 150 to 240 
centimetres in length may be stretched between the 

Science, 1906 



82 GENERAL PROPERTIES OF LIVING TISSUES 




THE GEAPHIC METHOD 83 

drums. Each drum is provided with an adjusting 
screw, by means of which the drum may be inclined until 
the strip of paper is stretched uniformly throughout its 
height. This adjustment should preferably be made 
upon the sliding drum. When the adjustment is 
complete, the abscissae drawn by a writing lever in 
successive revolutions will exactly coincide. The 
clockwork drum does not slide along the bench. 
Both drums may readily be removed from their 
bearings. 

Beneath the clockwork drum is a circular plate of 
the exact size of that of the medium spring kymo- 
graph. This plate rests on two feet and in fact 
supports the anterior end of the steel bench. The 
clockwork drum is driven by a kymograph in which 
the vertical steel drum-rod and sleeve are replaced by 
a short rod the top of which is flush with the upper 
plate of the kymograph. The feet of this kymo- 
graph are hollowed to tit three rounded pins. When 
the kymograph is set upon these pins, it is at once 
"centred" and all side motion is prevented. A 
coupling sleeve is now let down from the shaft of the 
clockwork drum until two projections on the under 
surface of the coupler engage with corresponding 
slots in the kymograph rod. The clockwork operates 
like that of the medium-spring kymograph, having 
ten changes of speed. The speeds are, however, 
faster as a stronger spring is used, the maximum 
being about seven centimetres per second. 

To smoke the paper, the coupler is raised, the 



84 GENERAL PROPERTIES OF LIVING TISSUES 

kymograph clockwork is removed, and then the entire 
bench together with its drums is placed horizontally 
in the smoker frame (Fig. 20). 




#5=> O 



Fig. 20. The smoker, showing the long paper kymograph in place. The 
paper is smoked with an oil lamp having a four inch wick. Near the 
stand are the handle with which the drum is revolved to carry the paper 
over the lamp flame, and the two rods which are inserted in the kymo- 
graph clockwork when the latter is used independently of the long paper 
arrangement. 

The graphic record involves the use of appa- 
ratus. It never should be forgotten that the use 
of apparatus always introduces more or less 
error. In every experiment the apparatus 
should be criticised sharply. The numerous 
imperfections which such scrutiny will bring 
to light are of two sorts, — the errors that may 
be neglected, and the errors that may not be 
neglected without seriously impairing the value 
of the method for the purpose in hand. For 
example, a count of the pulse rate with an ordi- 
nary watch will usually be incorrect by one or 



THE GRAPHIC METHOD 85 

two beats in the minute, but such a record is 
quite accurate enough for most purposes. The 
use of a stop-watch marking fifths of seconds 
would add nothing to the value of the count, 
for the error introduced by numberless causes 
that slightly modify the heart-beat from minute 
to minute is greater than the error introduced by 
using an ordinary watch instead of a stop-watch. 
The correction of errors that are too small to 
alter essentially the value of the method for 
the purpose to which it is applied is usually 
wasteful. 

With these points in mind, smoke a drum. 
Arrange the inductorium with simple key for 
maximal break induction currents. Prepare a 
gastrocnemius muscle, fasten it in the muscle 
clamp, tie a fine copper wire around the tendo 
Achillis, wrap the wire about the hook on the 
muscle lever, and fasten the end in the binding 
post of the muscle lever (Fig. 21). Connect 
the secondary coil with the posts on the muscle 
clamp and muscle lever respectively. Weight 
the muscle with ten grams. Arrange the lever 
to write on the drum. Record single contrac- 
tions with various speeds. 

Note that the muscle writes its contraction 
in the form of a curve, the ordinates of which 
measure the height to which the load is lifted. 



86 GENERAL PROPERTIES OF LIVING TISSUES 

Light Muscle Lever. 1 — A stout yoke (Fig. 21) 
bears two set screws holding a steel axle upon which 
is mounted a light piece of tubing and a hard-rubber 
pulley. One end of the tubing tapers slightly to 
receive the writing straw. The other projects behind 
the axle, and may be pressed upon by the accurately 
cut after-loading screw. The pulley is pierced with a 
hole for securing a fine wire by means of which a 




Fig. 21. The light muscle lever, with double hook straw fastener ; the 
actual size. 



weight may be suspended from the pulley when 
it is desirable that the weight should be applied 
near the axis of rotation. The muscle may also be 
weighted directly by means of a scale-pan suspended 
from the double ,hook to which the lower end of the 
muscle is attached. If the tendon of the muscle be 
fastened to the double hook by a fine wire, the free 
end of the wire may be carried to the insulated bind- 

1 First Catalogue of Harvard Physiological Apparatus, Sep- 
tember, 1901. 



THE GRAPHIC METHOD 87 

ing post provided for convenient electrical stimula- 
tion. The upper end of the muscle may be grasped 
in the flat-jawed clamp (Fig. 16), and thus connected 
electrically with the binding post upon it. 

In obtaining the extension curve of muscle this 
lever, after-loaded, may be weighted to one hundred 
grams without bending and thus deforming the curve. 
The abscissa will be a straight line. The moving 
parts are very light. The apparatus is compact and 
occupies but little of the vertical space so valuable 
where several recording instruments must be placed 
upon the same stand. 

Writing Lever. — A strip of aluminium, bent at 
one end to fasten with the double hook, pointed at 
the other, may be used in place of a straw. 

Tuning Fork. — A nickelled polished steel fork 
(Fig. 22) with steel handle is filed until it gives one 
hundred double vibrations per second. The tuning 
fork may be provided with a paper or foil writing- 



Fig. 22. The tuning fork ; about one-sixth the actual size. 

point and clamped to the iron stand. It serves to 
measure the latent period of muscular contraction and 
similar phenomena of brief duration. 

Start the drum at very rapid speed. Bring 
the writing point of the vibrating tuning fork 



88 GENERAL PROPERTIES OF LIVING TISSUES 

(Fig. 22) against the paper below the point of 
the muscle lever, and stimulate the muscle to 
contract. 

Observe that the tuning fork now gives the 
time intervals on the abscissa of the muscle 
curve, from which the duration of the periods 
of shortening and relaxation may be known. 
Note also the difference in appearance of curves 
recorded on a slow and a rapidly moving 
surface. 

Measure the interval between the beginning 
of contraction and the point of maximum 
shortening. 

In your laboratory note-book write a critical 
account of the muscle lever. 

Compare this account with the remarks which 
follow : — 

The object of the muscle lever is to write a 
magnified record of the change in form of the 
muscle. Usually the muscle is suspended in a 
muscle clamp and its lower end attached to 
the lever, which then records the shortening of 
the muscle. The same lever may be used to 
record the thickening of the muscle; in this 
case the muscle is of course horizontal and 
the lever rests upon it. For either purpose 
the weight of the lever is an objection, for 
it tends to prevent the muscle from begin- 



THE GRAPHIC METHOD 89 

ning its movement (inertia of position). Once 
in motion, the weight tends to keep moving, 
and thus to continue the record of contraction 
after the actual contraction has ceased (inertia 
of motion). As the inertia of motion increases 
with the mass and the square of the velocity, 
the lighter the lever the less the error. The 
disposition of the weight relative to the axis 
is also of importance. In a swinging system, 
the nearer the mass to the axis of rotation, the 
less are the after vibrations or pendulum-like 
oscillations which continue after the original im- 
pulse has ceased. For this reason, in experi- 
ments likely to be disturbed by after vibrations, 
the weight which the muscle lifts is attached 
to the small pulley, so as to be as near the 
axis as possible. In this case, the weight on 
the muscle is of course not the weight hung on 
the pulley; the pulley weight must be divided 
by the number of times the radius of the pulley 
is contained in the distance between the axis 
and the point of attachment of the muscle to the 
lever. 

It will be observed that the writing point is a 
strip of tinsel bent slightly and placed parallel 
to the writing surface. It is very easily moved 
in a direction at right angles to the writing sur- 
face, but resists movement in a vertical direction. 



90 GENERAL PROPERTIES OF LIVING TISSUES 

The bend makes the strip a weak spring, ena- 
bling the point to remain in contact with the 
drum throughout the excursion of the point on 
the paper. The writing point should be as nearly 
as possible parallel to the paper. Even in this 
position, the distance of the end of the straw 
from the paper is necessarily less when the lever 
is horizontal than when raised by the contrac- 
tion of the muscle, for the end of the lever 
describes a curved line in a plane tangent to the 
recording surface. Were it not for the spring 
of the writing point, the latter would leave the 
drum. To remain on the drum at the height of 
the contraction, the point must at the beginning 
of contraction press against the drum with much 
more friction than is necessary simply for scratch- 
ing through the layer of soot. Thus the distance 
of the writing point from the axis is constantly 
varying, and the magnification of the lever 
is constantly changing. Within the limits ordi- 
narily employed in physiology, the deformation 
of the curve thereby produced is proportional to 
the length of the arc through which the point 
moves ; the curve should therefore be written 
no larger than is necessary for clearness. 

When the smoked surface is at rest, and the 
contracting muscle lifts the lever, the writing 
point describes an arc ; when the muscle relaxes, 



THE GKAPHIC METHOD 91 

the writing point returns in the same line. When 
the drum revolves, the writing point describes a 
curve as the muscle contracts. The maximum 
shortening of the muscle, or height to which the 
load is lifted, is measured by a perpendicular 
drawn from the highest point of the curve to the 
abscissa. The time required for the muscle to 
reach this height, however, is not the distance on 
the abscissa from the beginning of the curve to 
the perpendicular, but to the point at which the 
segment of a circle of a radius equal to the 
length of the lever would cut the abscissa when 
drawn from the highest point of the curve. Prac- 
tically, this measurement is made by turning the 
drum back until the point of the raised lever 
rests at the summit of the curve, and then, 
while the drum is at rest, allowing the lever 
to write the ordinate by falling down to the 
abscissa. 

Perpendicular ordinates may be secured by a 
long pin passed transversely through the end of 
the writing lever, and bent twice at right angles, 
first parallel to the paper and then towards it. 
The lever is perpendicular to the paper and very 
near it; the weight of the pin keeps the point 
against the paper as the lever rises. The perpen- 
dicular writing has many faults in common with 
arc writing. 



92 GENERAL PROPERTIES OF LIVING TISSUES 



Apparatus 

Normal saline. Bowl. Pipette. Towel. Glass plate. 
Kymograph. Glazed paper. Smoking apparatus. Shel- 
lacking trough. Shellac in alcohol. Muscle lever (weight 
pan). Muscle clamp. Stand. Inductorium. Electrodes. 
Simple key. Dry cell. 5 Wires. Fine copper wire. Ten 
gram weight. Tuning fork. Tin foil. Cement. Frogs. 



STIMULATION OF MUSCLE AND NERVE 93 



IV 



THE ELECTRICAL STIMULATION OF MUSCLE 
AND NERVE 

The Galvanic Current 

The study of the changes occasioned in muscle 
and nerve by electrical stimulation may profit- 
ably begin with the action of the galvanic 
current. 

Non-Polarizable Electrodes. — When metal 
electrodes come in contact with an electro- 
lyte, polarization currents develop (see page 51). 
Electrodes of metal for this reason should be 
avoided in the study of the effect of the galvanic 
current on muscle and nerve. A "non-polar- 
izable" electrode should be employed. Strictly 
speaking, no electrode is non-polarizable, but 
practically the polarization errors are excluded 
by the device shown in Fig. 23. 

The boot electrodes (Fig. 23) are made of potter's 
clay, skilfully fired, and are unglazed. The leg is 
pierced with a hole 28 mm. deep and 8 mm. in 



94 GENERAL PROPERTIES OF LIVING TISSUES 

diameter, in which is placed the zinc. The foot is 
20 mm. long, measured from its junction with the 
leg. In the foot is a well for normal saline solution 
which shall keep the feet equally saturated. The 
boots should ordinarily be kept in normal saline so- 
lution. In use the hollow leg of the boot is half-filled 
with saturated solution of zinc sulphate and placed in 
the clip. The well in the foot of the boot is now filled 
with normal saline solution. If metal clips are used 




Fig. 23. Non-polarizable electrodes ; about 
two-fifths the actual size. 1 

the boots should be mounted on separate rods, to 
prevent the current passing through the unglazed 
boot to the metal holder and thus to the other boot. 
This difficulty is avoided by the rubber holders shown 
in Fig. 24. The electrodes may be mounted on a 
brass rod called the mounting-rod, or in the moist 
chamber shown in Fig. 24. The boot electrodes 
serve equally well for leading off the nerve or mus- 

1 First described in " Science," 1901, xiv, pp. 567-570. The 
well was added in Nov. 1905. 



STIMULATION OF MUSCLE AND NEEVE 



95 



cle current to the electrometer and for stimulation. 
After use, the boots should be emptied, rinsed in 
tap water, drained, and placed in several hundred 
cubic centimetres of normal saline solution until 
wanted again. If the foot of the boot is kept saturated 
with normal saline solution these electrodes will remain 




Fig. 24. The moist chamber ; about three-fifths the actual size. 

non-polarizable. They may also be used with normal 
saline clay. 

The Moist Chamber. 1 — The moist chamber (Fig. 
24) consists of a porcelain plate which bears near 

1 Science, 1901, n. s. xiv, p. 569. 



96 GENERAL PROPERTIES OF LIVING TISSUES 

the margin a shallow groove. In this groove rests a 
glass cover which for the sake of clearness has been 
omitted from the figure. To the porcelain plate is 
screwed a rod, by which the plate may be supported 
on a stand. Within the glass cover are two right- 
angled rods. One of the rods carries a small clamp, 
composed of a split screw on which moves a nut, by 
means of which the femur of a nerve-muscle prepara- 
tion may be firmly grasped. The holder for the split 
screw is arranged to permit of motion in all directions. 
Both right-angled rods carry unpolarizable electrodes. 
Each of these is borne by a hard-rubber holder. By 
turning the leg of the boot in the holder the foot may 
be brought as near the foot of the neighboring elec- 
trode as may be desired. It is desirable to mount 
the boots on opposite rods as in Fig. 24. A thick 
wire of freshly amalgamated zinc, provided at one 
end with a hole in which a connecting wire may be 
fastened with a set screw, is placed in the leg of the 
boot, and the other end of the connecting wire 
brought to one of the four binding posts shown in 
Fig. 24. These four posts are in electrical connec- 
tion with four other posts beneath the porcelain 
plate. The air within the moist chamber may be 
kept saturated with water vapor by applying moist 
filter paper to the inner side of the glass globe. 

Destruction of the Brain by Pithing. — The 

next experiment requires a curarized muscle, and 



STIMULATION OF MUSCLE AND NERVE 97 

curarization is best accomplished by the injec- 
tion of curare into the dorsal lymph sac of a 
frog the brain of which has been destroyed. 
Wrap the frog in the cloth, head out. Hold the 
frog with the fingers of the left hand, pressing 
down the tip of the frog's nose with the left 
thumb. Pass the right forefinger along the mid- 
dle line of the head. A slight depression will be 
felt at the joining of the skull and trunk. Here 
the cerebro -spinal canal has no bony covering. 
Make at this point a cut about a centimetre 
(I inch) long through the skin in the middle line. 
Thrust the seeker vertically through the soft 
tissues until the point is stopped by the bony 
vertebrae. Turn the point of the seeker towards 
the head, and push it along the brain cavity, 
moving it gently from side to side. 

Paralysis of Voluntary Motion by Curare. — 
Make a very small hole in the skin of the back 
into the dorsal lymph sac. With a fine glass 
pipette inject a few drops of a straw-colored 
solution of curare. The curare of commerce is 
the dried juice of a species of strychnos. It is 
not a definite chemical compound and cannot 
therefore be given in an accurate dose. It is 
customary to make a one per cent solution of the 
crude mass. This solution may be kept from 

7 



98 GENERAL PROPERTIES OF LIVING TISSUES 

decomposition by a small crystal of thymol. The 
bottle should be shaken before the curare is with- 
drawn. The curare should be injected at the 
beginning of the laboratory day, so that there 
may be time for its action in a dilute solution. 
The motor nerves are paralyzed first and the 
effect should, if possible, be limited to them. 
Strong solutions paralyze other nerves, the heart, 
and probably other muscles. 

Opening and closing Contraction. — Place two 
non-polarizable boot electrodes in rubber holders 
upon a mounting-rod. Fill the boots half full 
of saturated solution of zinc sulphate. Fill the 
well in the toe of each boot with normal saline 
solution. Place well amalgamated zincs in the 
boots and connect them through an open simple 
key with the poles of a battery. Prepare a 
sartorius muscle (Fig. 25) from a curarized frog, 1 
preserving the pelvic and tibial attachments. 
Lay the muscle upon the toes of the boot 
electrodes. Close the key. 

The muscle will twitch when the current is 
made and probably when it is broken, but during 
the passage of the current there will be normally 
no contraction. 

1 Be sure to cut off the head or otherwise destroy the brain 
of curarized frogs before operating on them. 



STIMULATION OF MUSCLE AND NERVE 



99 



In frogs used during the period of hibernation 
and especially in those brought from a cold store- 
room into a warm laboratory, the make and some- 
times the break of the constant current may be 
followed by prolonged 
tetanus. In such frogs, 
the irritability of the 
muscles is greatly 
increased, and the 
changes, probably 
ionic, which occur 
while the current is 
passing and after it is 
shut off are sufficient to 
produce contractions 
not seen in the normal 
state (see page 147). 
Usually the muscle is 
stimulated only by a 
sudden change in the Fi s- 25 - Hiud limb of fr °s> anterior 

view (Eeker-Wiedersheim). 

intensity of the current. 

Changes in Intensity of Stimulus. — Connect 
one of the electrodes used in the preceding ex- 
periment with one of the poles of a dry cell. 
From the other pole lead a wire to a bowl of 
salt water. To the other side of the same bowl 
bring a wire from the remaining electrode. 

When the wires are slowly brought nearer 




t.a. 



100 GENERAL PROPERTIES OF LIVING TISSUES 

together, there will be no contraction ; when they 
are brought quickly together, thus quickly in- 
creasing the intensity of the current, the muscle 
will contract. 

With Indirect Stimulation. — 1 . Smoke a drum. 
Make a nerve-muscle preparation (sciatic nerve 
and gastrocnemius muscle). Place the femur 
in the clamp in the moist chamber. Let the 
nerve rest on non-polarizable electrodes connected 
through an open key with a dry cell. Attach 
the tendo Achillis to the muscle lever. Let the 
muscle lever write on a slowly moving drum. 
Close and open the key. 

Both closing and opening contraction will be 
seen. (If the frog has been brought from a cold 
room into the warm laboratory, opening and 
closing tetanus will probably replace the usual 
twitch. See page 147.) 

2. Repeat the experiment on page 99, using 
the nerve-muscle preparation instead of the 
curarized muscle. 

It will again be found that the intensity of 
the current must be increased with a certain 
rapidity in order to stimulate. 

The experiments just made support DuBois- 
Reymond's statement that the electrical current 
does not stimulate during the entire period of 
its flow through the irritable tissue, but only 



STIMULATION OP MUSCLE AND NERVE 101 

when the intensity is rapidly altered by making 
or breaking the circuit. These experiments, 
however, were made on the rapidly reacting 
skeletal muscle of the frog. The law does not 
hold good for sluggish contractile tissue. In- 
deed it can be disproved even for highly striated 
muscle by a very careful examination of the 
manner in which excitation takes place. Pnuger 
discovered that when the galvanic current is 
made, excitation takes place only at the points 
through which the current leaves the muscle or 
nerve (cathodal stimulation), and that when the 
current is broken, excitation takes place only 
where the current enters the irritable tissue. 
This "polar excitation" we must now consider. 
We shall find, among many other facts, the 
refutation of the idea that stimulation does not 
occur throughout the passage of the current. 

Polar Stimulation of Muscle 

1. Slit the curarized sartorius muscle trouser- 
like from the lower end. Lay each end on a 
boot electrode. Make and break the current. 

On making the current the cathodal side will 
contract ; on breaking, the anodal side. 

2. Lay the muscle on ice covered with a small 
piece of paraffin paper, to shield the muscle from 



102 GENERAL PROPERTIES OF LIVING TISSUES 

water. When thoroughly cold, place the muscle 
in the Gaskell clamp (Fig. 26), making very 
gentle pressure across the middle, and bring the 
non-polarizable electrodes against the ends. Make 
and, after a minute, break the current. 

The excitation wave passes so slowly through 
cooled muscle that the contraction can be seen 
with the unaided eye to begin at the cathode on 
closing and at the anode on opening the circuit. 

3. Ureter. 1 — Place the extirpated ureter of 
any mammal on a glass plate set as a cover on 
a beaker containing hot normal saline solution, 
so that the hot vapor of the water shall keep 
the ureter warm. Bring the non-polarizable 
electrodes against the ureter. Note which elec- 
trode is the cathode. Close the key. 

After a distinct latent period the ureter in the 
cathodal region, and nowhere else, will contract, 
and the contraction wave will spread from the 
cathode in both directions along the ureter. 

Open the key. 

The Gaskell Clamp. — The tapered edge of a hard- 
rubber block is brought against a similar edge by 
means of a fine screw (Fig. 26). With this clamp 
the heart muscle may be compressed, after Gaskell's 

1 The experiment succeeds also with extirpated pieces of in- 
testine about four inches long, provided they are kept warm 
with normal saline solution. 



STIMULATION OF MUSCLE AND NERVE 103 

method, until conduction between auricle and ven- 
tricle is partially or wholly interrupted. The clamp 



QO~fe 



Fig. 26. The Gaskell clamp ; about one-third the actual size. 1 

is also used to press upon the sartorius until the con- 
duction wave is blocked while the excitation wave 
still passes. 

The contraction takes place now only at 
the anode, and the contraction wave spreads 
from that point over the muscle (as making 
the current is a less effective stimulus than 
breaking it may be necessary to increase the 
strength of the current, or to keep it closed a 
considerable time, in order to secure making 
contraction). 

4. Intestine. — Place the non-polarizable anode 
on the intestine of a freshly killed rabbit or frog, 
the cathode on some indifferent point, for example 
the liver. Close the key. 

The intestine will constrict in the anodal re- 
gion and remain constricted during the passage 
of the current, provided it be not so long as to 

1 This form was first described in the Catalogue of the Harvard 
Apparatus Company, May, 1905. 



104 GENERAL PROPERTIES OF LIVING TISSUES 

cause fatigue. A peristaltic contraction wave 
usually passes from the anode in both directions 
along the intestine. 

Place the cathode on the intestine, and the 
anode on an indifferent point. Close the key. 

A small, indistinct thickening will be seen in 
the cathodal region. 

Thus the intestine, while it serves admirably to 
illustrate a polar action of the galvanic current, ap- 
parently differs from the tissues already considered 
in that closure causes contraction at the anode in- 
stead of the cathode. The exception is only appar- 
ent, and its explanation is that the point at which 
the electrode touches the peritoneal surface of the 
many-layered intestinal wall is not the physiologi- 
cal anode or cathode ; i. e. not the point at which 
the current actually enters or leaves the muscular 
coat. This matter is discussed on page 110. 

5. Smoke a drum. Eaise the drum off the fric- 
tion bearing by turning the screw at the top of the 
shaft to the right. Arrange two muscle levers 2 
and the electro-magnetic signal (Fig. 27) to write 
on the drum in the same vertical line. Place the 
electro-magnetic signal, together with a simple 
key, in the circuit between one dry cell and the 
rheochord. Bring the slider near the positive 
post of the rheochord. 

1 Or heart levers (Fig. 53, page 311). 



STIMULATION OF MUSCLE AND NERVE 105 




< 1 



Fig. 27. The signal magnet ; the actual size. 

The Electro-magnetic signal. 1 — A protecting metal 
box (Fig. 27), open at the front and ends, contains a 
strong magnet, the armature of which is mounted upon 
a steel spring. An accurate fine adjustment screw reg- 
ulates the excursion of the armature. One binding 
post is mounted upon the metal box, the other is insu- 
lated by a rubber block. This signal, in circuit with a 
vibrating tuning fork, will record one hundred double 
vibrations per second. In the primary circuit of the 
inductorium it will record the make and break of the 
current without after-vibrations which are prevented by 
lead foil placed on the spring where it strikes the limit- 
ing screw. Residual magnetism is obviated by parch- 
ment paper, fastened to the spring with shellac at the 
point where the spring would touch the core of the 
magnet. The handle is long enough to bring the writ- 
ing point directly above or below the writing point of 
the muscle lever clamped to the same iron stand. 

The metal box is of soft iron and serves as an 
extension of the magnet core, thus completing the 
magnetic circuit, and doing away with a second spool. 
The magnetic power is further improved by boring 
out the core, which is then " softened " by heat. 

1 First Catalogue of Harvard Apparatus, September, 1901, p. 46. 



106 GENERAL PROPERTIES OF LIVING TISSUES 

Fasten a curarized sartorius muscle by the middle 
in the Gaskell clamp ; the pressure should be 
enough to prevent the contraction wave of one 
part reaching the other part, but not great enough 
to prevent the passage of the excitation. Place 
the muscle vertical to the writing levers. Tie a 
thread around the pelvic and tibial fragments 
and fasten each thread to a muscle lever, so that 
each half of the muscle may record its contrac- 
tion independently of the other. Moisten two 
strands of lamp wick with normal saline clay. 
Tie one strand around each end of the muscle 
and lay the free portion of the strands on the 
toes of boot electrodes properly mounted. Note 
which lever is connected with the cathodal end. 
Make the current. If the muscle does not con- 
tract, move the slider along the wire a short dis- 
tance towards the positive post (so as to bring 
a stronger current through the electrodes) and 
make the current again. When both make and 
break contractions are secured, see that the writ- 
ing points record properly, and " spin " the drum, 
but not too fast. As soon as the drum moves 
steadily, make and then break the current. 

The moment of making and breaking the cur- 
rent will be recorded by the electro-magnetic 
signal. An instant later the muscle levers will 
begin their record of the contractions. 



STIMULATION OF MUSCLE AND NERVE 107 

It will be found that the cathodal half of 
the muscle contracts first on closing, the anodal 
half on opening the circuit. Evidently the 
excitation began on closure at the cathode and 
passed thence to the anode, while on opening 
the circuit the excitation began at the anode 
and passed to the cathode. 

In order to measure this interval accurately 
the drum should be turned back until the writ- 
ing point of the signal lies precisely in the ordi- 
nate drawn by it during the experiment. The 
muscle should then be stimulated. The ordinate 
now drawn by the muscle with the drum thus 
at rest will be synchronous with that drawn by 
the signal during the experiment, and will mark 
upon the abscissa of the muscle curve the moment 
of stimulation, 

6. Tonic Contraction. — Connect a dry cell 
through an open simple key with the metre 
posts of the rheochord. Connect non-polarizable 
electrodes with the positive post and the slider. 
Fasten one end of the curarized sartorius (pre- 
pared with fragments of pelvis and tibia attached) 
in the muscle clamp. Tie a thread to the other 
end and fasten the thread to the upright pin of 
the muscle lever. Let non-polarizable electrodes 
rest on the muscle near the respective ends. 
Use a strength of current that will just cause 



108 GENERAL PROPERTIES OF LIVING TISSUES 

contraction on closure. Watch very closely the 
cathodal region near the junction of the muscle 
fibres with the tendon. Close the key. 

After the closing contraction, the ends of the 
muscle fibres next the tendon in the cathodal 
region will show a faint but distinct thickening, 
which will remain until the current is broken. 

These several experiments demonstrate that in 
galvanic stimulation of both skeletal and smooth 
muscle the excitation takes place at the points 
where the current leaves and enters the muscle. 
Before inquiring whether this law holds good for 
the heart, the muscle cells in which have a form 
intermediate between the smooth muscle cell and 
the cells of skeletal muscle, it will be necessary 
to consider whether the points of contact with 
the electrodes are always the real anode and 
cathode. 

Physiological Anode and Cathode. — When the 
electrodes are placed directly on a nerve, or are 
applied to a muscle with straight parallel fibres in 
such a way that the current flows through each 
fibre from end to end, the anode and cathode 
obviously coincide with the points at which the 
electrodes touch the muscle. When, however, 
the fibres are of irregular shape, or are irregularly 
disposed, the current lines can no longer traverse 
the fibres from end to end, but will enter and 



STIMULATION OF MUSCLE AND NERVE 109 

leave fibres at points other than those in contact 
with the electrodes. 

The difference between the operator's elec- 
trodes and the physiological anode and cathode 
is also obvious when the electrodes are applied 
to skin, connective tissue, mucous membrane, etc. , 
covering the muscle or nerve, — the points at 
which the electrodes touch the covering tissue 
cannot be the points at which the current actu- 
ally leaves or enters the muscle. 

The failure to keep this distinction in mind 
may lead to wholly erroneous interpretations. 
Thus when the ureter is extirpated, or is raised 
from the tissues on which it normally rests, its 
reaction to the galvanic current follows the law, 
— contraction begins at cathode on making, at 
anode on breaking the current; but when the 
ureter is stimulated in situ, exactly the opposite 
effect is seen, — contraction begins at anode on 
making the current. The explanation is that 
the current lines in the latter case are very 
widely diffused through the conducting tissues 
on which the ureter lies, so that the current 
passes into and out of the muscle fibres for some 
distance either side of the positive electrode. 
Each point at which the current leaves a fibre 
is a secondary cathode, and if the number of 
such points is large, cathodal stimulation will 



110 GENERAL PROPERTIES OF LIVING TISSUES 

take place in what, superficially regarded, is the 
anodal region (compare page 131, and Fig. 37). 
The same explanation holds good for the intes- 
tine (see page 103). The formation of physio- 
logical anodes and cathodes is well shown in the 
next experiment. 

Physiological Anodes and Cathodes in Rectus 
Muscle. — Eemove the rectus abdominis muscle, 
from a curarized frog. Note the tendinous cross 
bands which divide the muscle from side to 
side and divide it into parts. Lay the muscle 
smoothly on a glass slide. Connect the non- 
polarizable electrodes through a simple key with 
a dry cell. Place one electrode on each end of 
the muscle. Close the key. 

On closure, the cathodal side of each division 
of the muscle will show a sharply defined con- 
tinued contraction of the ends of the fibres at 
their insertion in the transverse tendinous bands. 
On opening, the cathodal contraction disappears, 
and a similar thickening of the fibres is seen at 
the anodal side of each division. The twitch of 
each segment on closure and opening of the cur- 
rent also starts respectively from the cathodal 
and anodal ends of each segment. These effects 
are best seen through a magnifying glass. 

Polar Stimulation in Heart. — The muscle cells 
of the heart are not only of irregular shape, but 



STIMULATION OF MUSCLE AND NERVE 111 

they are so joined with each other as to make it 
impossible to pass a current through the heart 
muscle without the current lines cutting fibres 
in every direction. It would seem therefore that 
secondary anodes and cathodes would be formed 
to such a degree that the demonstration of polar 
excitation would be difficult or impossible. Ex- 
perimentation shows however that this is not the 
case. The heart behaves like a single hollow 
fibre. 

Monopolar Method. — The small size and conical 
form of the ventricle of the frog's heart make the 
ordinary method of stimulation, in which the 
electrodes would both be placed on the heart, 
less suitable than the monopolar method. This 
method was suggested by the fact that the 
stimulating effect of the galvanic current depends 
on its density. If one electrode has a large sur- 
face, and the other a very small surface, the 
current lines will be distributed through a con- 
siderable cross-section in the first instance and 
converge to a small cone in the second. The 
threshold value of stimulation will not be 
reached at the large electrode, and stimulation 
will occur only at the small electrode. Thus the 
large "indifferent" electrode may be placed on 
any part of the frog's body, and the convenient 
small electrode be used to stimulate the heart. 



112 GENERAL PROPERTIES OF LIVING TISSUES 

Cover the indifferent electrode (consisting of a 

brass plate furnished with a binding post) with 

cotton wet with saline solution. Mount a non- 

polarizable boot electrode. Con- 

/ nect a dry cell with the metre 

posts (0 and 1) of the rheochord 

through a simple key (Fig. 28). 

Connect post and the slider 

through a pole-changer (with 

\^ ^ / °^° cross-wires) with the electrodes. 

^ Expose the heart, according 

to the following method : 

Place the brainless frog, back down, in the 

holder (Fig. 29). Cut through the skin across 

the middle of the body from side to side. 

Make a second cut in the middle line from the 




Fig. 29. The frog board, with spring clips ; about one-fourth the actual 
size. 

first cut to near the lower jaw. Turn back the 
flaps. Cut through the sternal cartilage near its 
lower end, thus avoiding the epigastric vein. 



STIMULATION OF MUSCLE AND NERVE 113 

Cautiously remove the breast bone, doing no 
harm to deeper parts. Open the delicate mem- 
brane (pericardium) which surrounds the heart. 
Tie a ligature about the sinus-auricular junction, 
to stop the ventricular contractions. Place the 
indifferent electrode over the larynx and the non- 
polarizable electrode on the ventricle. Turn the 
pole-changer so that the electrode on the heart 
becomes the anode. Close and then open the 
key. 

Contraction will take place on opening only, 
if at all. Eeverse the pole-changer so that the 
cardiac electrode becomes the cathode. Close 
and then open the key. 

Contraction takes place at closure only. 

Polar Stimulation of Nerve 

Law of Contraction. — 1. Whether contraction 
will follow the galvanic stimulation of a motor 
nerve depends on the irritability of the nerve 
and the direction and intensity of the current. 
The current may pass through the intrapolar 
portion of the nerve towards the muscle (de- 
scending current) or away from it (ascending 
current). The intensity may be weak, medium, 
or strong ; intensity in this case is evidently 
merely a relative term, depending on the irrita- 



114 GENERAL PROPERTIES OF LIVING TISSUES 

bility of the particular nerve in hand. We will 
test first the effect of the ascending current. 

Connect a dry cell through an open key with 
the metre posts of the rheochord (Fig. 30). Join 
the positive post and the slider through a pole- 
changer (cross-wires in place), with the non- 
polarizable electrodes placed in the moist 







'.^v 



Fig. 30.1 

chamber (Fig. 24, page 95), in the holders farthest 
from the opening for the muscle. Make a 
nerve-muscle preparation. Secure the femur in 
the femur clamp of the moist chamber. Let 
the nerve lie on the non-polarizable electrodes. 
Attach the Achilles tendon to the muscle lever. 
Keep the air in the chamber moist by lining 
the glass shade with filter paper saturated with 
water. Arrange the pole-changer so that the 

1 The inductorium shown in Fig. 30 is not used in this ex- 
periment, but in the first experiment on page 116, 



STIMULATION OF MUSCLE AND NERVE 115 

anode shall be next the muscle. Move the slider 
near the positive post. Make and break the gal- 
vanic current. If no contraction is secured, 
move the slider to increase the current, and 
repeat the experiment. 

The first contraction will take place on mak- 
ing the current. Continue to increase the cur- 
rent strength by moving the slider. 

A point will be reached at which contraction 
will occur both on opening and closure. 

Increase the intensity of the current by add- 
ing dry cells in series (zinc to carbon), testing 
the effect after each addition by closing and 
opening the current. 

An intensity will be reached at which opening 
and not closure causes contraction. 

In a similar manner, work out the law of con- 
traction for descending currents. (It may be 
necessary to take a fresh nerve-muscle prepa- 
ration.) 

Set down the results in a table. 

Intensity Ascending current. Descending current, 

of current. Make. Break. Make. Break. 

"Weak. Contr. Rest. Contr. Rest. 

Medium. Contr. Contr. Contr. Contr. 

Strong. Rest. Contr. Contr. Rest (Weak contr.). 

2. The remarkable nature of these results is 
apparent on observing that contraction is easily 



116 GENERAL PROPERTIES OF LIVING TISSUES 

secured on closing a weak ascending current and 
yet cannot be obtained with a strong one. The 
first step in the inquiry into the causes of the 
phenomena is to determine whether the stimu- 
lation is polar. That the nerve impulse really 
starts at the cathode on closure and at the anode 
on opening is shown (1) by the fact that the 
interval between stimulation and contraction, 
with the ascending current, in which the anode 
is next the muscle, is longer at closure than on 
opening, while the opposite is the case when the 
current is descending. (2) With descending 
currents, it sometimes happens that opening 
produces tetanus instead of a simple twitch. 
If this tetanus appears, the student should sever 
the nerve between the electrodes. Immediately 
the contractions will cease. They must there- 
fore have arisen at the anode, for the cathode 
still remains in full connection with the muscle. 

Changes in Irritability. — The second step in 
this inquiry is to determine the nature of the 
changes at the poles. For this purpose the 
nerve should be stimulated in the cathodal and 
anodal regions during the passage of the constant 
current. 

1. Pass two needles through a cork placed in 
the rubber holder next the muscle in the moist 
chamber. Connect them with the secondary coil 



STIMULATION OF MUSCLE AND NERVE 117 

of an inductorium (Fig. 30). Arrange the pri- 
mary for single induction shocks, which must 
not be maximal. Turn the pole-changer to bring 
the cathode next the metal electrodes. Using a 
weak induction current as stimulus, record on a 
stationary drum three contractions: (1) before 
the passing of the galvanic current through 
the nerve, (2) during its passage, (3) after its 
passage. 

The second contraction — that obtained by 
stimulating in the cathodal region during the 
passage of the galvanic current — will be greater 
than the other two. 

Eeverse the galvanic current and repeat the 
experiment, the stimulation now being in the 
anodal region. 

The stimulation in the anodal region during 
the passage of the galvanic current causes less 
than the normal contraction. 

2. The stimulating current may be superposed 
directly on the polarizing current by using the 
same electrodes. 

Connect a dry cell through an open key with 
the and 1 metre posts of the rheochord 
(Fig. 31). Connect the positive post of the 
rheochord with one of the non-polarizable elec- 
trodes. Join the slider to one end of the second- 
ary wire of an inductorium ; to the other end 



^cra~~ r— ••■••: a,-. : .v..v 



118 GENERAL PROPERTIES OF LIVING TISSUES 

join the remaining non-polarizable electrode. If 

the positive pole of the secondary coil is not 

known, determine it by the electrolytic method 

(page 158). Arrange the primary coil of the 

inductorium for single 

' c— »*-rv submaximal induction 

\/ currents. Make and 

break the induction 

current, and record 

Ks*--... '-L. y ! the contractions on 

s Sq) — ' 

^ the drum. Now pass 

a weak polarizing cur- 
rent through the nerve and stimulate again with 
the induction current. 

It will be found that the stimulating effect of 
the induction current is increased when the 
direction of the induction current coincides with 
that of the polarizing current, i. e. when the 
cathode (which is the sole source of the induc- 
tion stimulus, as pointed out on page 160) coin- 
cides with the cathode of the polarizing current. 
When the cathode of the induction circuit falls 
in the anodal region of the polarizing circuit, the 
stimulating effect is diminished. Very strong 
polarizing currents produce such alterations in 
irritability that the additional alteration caused 
by the brief induction current is not great enough 
to be a stimulus. 



STIMULATION OF MUSCLE AND NEEVE 119 

The law revealed by this experiment may be 
thus expressed. The same stimulating current 
has a greater stimulating effect when it coincides 
in direction with a pre-existing current, and a 
lessened effect when it is opposed in direction to 
a pre-existing current. This law explains the 
interference observed between stimulating cur- 
rents and demarcation or injury currents of nerve 
and muscle (see page 292). 

3. Place a drop of saturated solution of sodium 
chloride on the nerve in the extrapolar region 
near one of the non-polarizable electrodes. 
Eecord the irregular tetanus (chemical stimu- 
lation) on a slowly moving drum. Make the 
polarizing current. 

Note that the tetanus is increased when the 
cathode is nearer the stimulating solution, but 
diminished when the anode is nearer. 

Hence the irritability of the nerve is altered 
during the passage of the electric current (elec- 
trotonus); 1 it is increased in the neighborhood 
of the cathode (catelectrotonus) and is diminished 
in the neighborhood of the anode (anelectro- 

1 The change in the excitability of the nerve produced by 
the electric current is so generally called electrotonus that the 
term cannot well be changed. It should not be confused with 
the electrotonus described on page 000, though it is possible 
that the two phenomena have a similar if not identical first 
cause. 



120 GENERAL PROPERTIES OF LIVING TISSUES 

tonus). In the intrapolar region, the cathodal 
touches the anodal area at the so-called indifferent 
point. This point approaches the cathode when 
the intensity of the polarizing current is increased. 

The greater the length of nerve between the 
electrodes, the greater the extrapolar electrotonus. 
Catelectro tonus rises rapidly to a maximum as 
soon as the circuit is closed, and then gradually 
wanes. Anelectrotonus develops more slowly and 
does not reach its maximum for some time after 
closure. 

On the opening of the circuit, the conditions at 
the anode and cathode are reversed, the irritability 
falls at the cathode and rises at the anode. The 
fall in the cathodal region is of short duration 
and the irritability soon returns again towards 
normal. In the anodal region, the rise on open- 
ing is unbroken. 

Changes in Conductivity. — We have seen 
that the irritability is altered by the galvanic 
current. The conductivity also is altered. 

Connect a dry cell through a pole-changer with 
cross-wires to a pair of non-polarizable electrodes 
placed in the holders of the moist chamber 
farthest from the muscle (Fig. 32). Leave one 
wire uncoupled until the current is wanted. 
Connect another cell with the primary coil of 
the inductorium arranged for break induction 



STIMULATION OF MUSCLE AND NERVE 121 



shocks, placing in the circuit a simple key and 
the electro-magnetic signal. Lead wires from the 
poles of the secondary coil to the side cups of a 
pole-changer (without cross-wires). In each of 
the remaining two holders of the moist chamber 
place a cork pierced by two metal electrodes. 
One wire in each pair should be insulated from 
its fellow by rubber 
tubing drawn over the 
part between the cork 
and the end of the elec- 
trode to be applied 
to the nerve. Connect 
the wire soldered to 
the basal ends of these 
electrodes with the re- 
maining cups of the 
pole-changer in the sec- 
ondary circuit of the 
inductorium. Arrange the signal to write on the 
smoked drum beneath the writing point of the 
muscle lever. 

Make a nerve-muscle preparation. Let the 
nerve rest on the non-polarizable electrodes near 
the cross-section. Place one pair of the metal 
electrodes beneath the nerve near the muscle, the 
other pair near the non-polarizable electrodes. 
The clockwork of the drum should be fully 




*Q <=$ 



Fig. 32. 



122 GENERAL PROPERTIES OF LIVING TISSUES 

wound (not over- wound), and the drum should 
revolve at its most rapid speed. Write two 
muscle curves. For the first stimulate through 
the metal electrodes nearer the muscle ; for the 
second through the metal electrodes farther from 
the muscle. 

While each curve is writing, let a tuning fork 
record its vibrations beneath the point of the 
the muscle lever. To mark on the abscissa of 
the muscle curve the exact moment at which the 
muscle was stimulated, turn back the drum until 
the writing point of the signal lies precisely in 
the line described by it when the current was 
broken. Now stimulate the muscle with another 
induction shock. The curved ordinate of the 
muscle lever will be synchronous with the ordi- 
nate of the signal. 

The interval between the moment of stimula- 
tion, as recorded by the signal, and the beginning 
of contraction, is greater when the nerve is stim- 
ulated far from the muscle. The difference is 
the time required for the nerve impulse to tra- 
verse the length of nerve between the electrodes, 
provided of course that the interval between the 
arrival of the nerve impulse in the muscle and 
the beginning of the contraction is the same in 
both cases, an assumption considered reasonable 
by most physiologists. 



STIMULATION OF MUSCLE AND NERVE 123 

Write now three other pairs of curves : one 
while a galvanic current passes through the non- 
polarizable electrodes in a descending direction 
(cathode nearer the muscle); a second while an 
ascending current passes (anode nearer the mus- 
cle) ; and a third, after the galvanic current has 
been some minutes broken, as a control. During 
the writing of these curves measure the velocity 
of the drum with the tuning fork as before. 

The speed of the nerve impulse will be found 
to be greater than normal when the nerve im- 
pulse starting at the second pair of metal elec- 
trodes passes through an extrapolar cathodal 
area (i. e. stimulation during descending current), 
and less than normal when that region is made 
anodal by reversing the galvanic current. In 
other words, the conductivity of the nerve has 
been increased by cathodal and diminished by 
anodal stimulation. 

2. Conductivity is diminished by strong or pro- 
tracted currents in the cathodal as well as in the 
anodal region. — Place two non-polarizable elec- 
trodes upon the nerve about 3 cm. apart. Con- 
nect them through a pole-changer with two dry 
cells (Fig. 33). In the middle of the intra polar 
region place two stimulating electrodes close 
together. Connect one of the stimulating elec- 
trodes directly to the secondary coil of an indue- 



124 GENERAL PROPERTIES OF LIVING TISSUES 

torium arranged for single induction currents. 
Lead from the other stimulating electrode to a 
piece of nerve or muscle about 4 cm. long, and 
thence to the secondary coil. The introduction 
of this great resistance will keep most of the 
polarizing current in the short bridge of nerve 
between the polarizing electrodes. Without this 
resistance, the polarizing current would pass 
^ through the stimulating 

r<^ ^-A : circuit in preference to 

X 'X/0\/ crossing the nerve be- 

x5< tween the stimulating 

i L-^_ electrodes. Observe that 

•-— -^..v the nerve impulse cre- 

ated by the stimulus 
must pass through the 
Fig. 33. cathodal region, if the 

current be descending, or 
the anodal region, if the current be ascending, in 
order to reach the muscle. 

Find the position of the secondary coil at 
which the muscle will barely contract on making 
the stimulating current. Arrange the pole- 
changer to bring the anode between the stimu- 
lating electrodes and the muscle, and make the 
polarizing current. Stimulate with a make in- 
duction current during the passage of the polar- 
izing current. Open the polarizing current. 



" t= KLy^> 



STIMULATION OF MUSCLE AND NERVE 125 

After three minutes' rest, bring the cathode next 
the muscle and make the polarizing current as 
before. Then stimulate again with a make in- 
duction current of the same intensity as before. 

Contraction will be absent, or at most very 
weak. The impulse will be blocked in the 
cathodal region. In truth, during the passage of 
strong or protracted currents, the conductivity is 
more diminished in the cathodal than in the 
anodal region. 

Grutzner and Tigerstedt believe that the open- 
ing contraction is due to the stimulation of the 
nerve or muscle by the polarization current 
which appears when the galvanic current is 
broken. The polarization current may be said 
to be closed when the galvanic current is opened. 
These observers, therefore, hold that stimulation 
takes place only at closure. 

We are now in a position to account for the 
phenomena described by the law of contraction. 
The irritability of the nerve is increased at the 
cathode on closing, and at the anode on opening 
the galvanic current. This rise of irritability 
stimulates the nerve. The rise at the cathode is 
a more effective stimulus than the rise at the 
anode ; consequently with weak currents the first 
stimulus to produce contraction is cathodal, i. c. 
at the closure of the circuit. As the current in- 



126 GENERAL PROPERTIES OF LIVING TISSUES 

tensity is increased, the anodal rise becomes also 
effective, and contraction is secured by both mak- 
ing and breaking the current. 

But we have to deal also with a decrease in 
irritability, and, still more important for the 
explanation of the effects of strong currents, with 
a decrease in conductivity. The irritability and 
conductivity are decreased on closure at the anode 
and on opening at the cathode. If the anode is 
next the muscle (Fig. 34), the decrease in con- 
ductivity on closure of a strong 
current will block the nerve im- 
^ 3 *-^ pulse coining from the cathode; 
it will therefore never reach the 
<C3 — | *~| ■ muscle, and there will be no 
Fig. 34. contraction on closure. If the 

cathode is next the muscle, the 
conductivity may be so decreased on opening that 
the nerve impulse coming from the anode may be 
blocked. The decrease at cathode, when the cur- 
rent is broken, is, however, less marked than the 
decrease at anode when the current is made, so 
that the cathodal decrease, even w x ith strong 
currents, sometimes fails to block the impulse 
entirely. In that case, a weak contraction may 
be obtained at the break of the descending 
current. 



stimulation of muscle and nerve 127 

Stimulation of Human Nerves 

Duchenne devised a method by which either the 
motor or the sensory human nerves can be stimu- 
lated at will, and the reaction of single muscles 
or groups of muscles to electricity determined. 
When electrodes are placed on the surface of the 
skin and the circuit is made, the current entering 
at the anode will spread in current lines through 
the entire body. At the cathode, all these lines 
will converge again. The density of the current 
depends on the concentration of the current 
lines. Thus the density is relatively great at 
the electrodes, and becomes rapidly weaker as 
the lines diverge between them. The smaller the 
electrode, the greater the density. The stimulat- 
ing effect depends on the density. With small 
electrodes, a current not sufficient to cause stimu- 
lation may gradually be increased in strength 
until the density at the electrode becomes great 
enough to stimulate, while in all other regions it 
is not yet great enough. Thus a local stimula- 
tion is secured. But this local stimulus does 
not sufficiently distinguish between the sensory 
nerves and the motor nerves and muscles ; for in 
order to reach the deeper lying motor nerves and 
muscles, the current must pass through the skin. 
The resistance of the epidermis is very great, aud 



128 GENERAL PROPERTIES OF LIVING TISSUES 

currents of considerable intensity are necessary 
to overcome it. Once through the epidermis, the 
current spreads immediately in all directions 
through the cutis, where it stimulates the very 

Mm. lumbricales 



M. opponens digit, min. 

M. flexor digit, min. 

M. abd. digit, min. 

M. palmaris brevis 

N. ulnaris (ram. vol. 
prof.) 

N. medianus 

M. flexor digit, subl. 
(ind. and minim.) 

M. flexor, digit, subl. 
(II & III) 



M. flexor digit profund. 

M. ulnaris internus 

(flexor carp, uln.) 

M. palm, longus 

M. pronator teres 

N. medianus 




M. adductor poll. 
M. flexor poll, brevis 
M. opponens pollicis 
M. abductor poll, brevis 



M. flexor pollicis longus 



M. flexor digit, subl. 



M. rad. internus (flexor 
carp, rad ) 

M. supin. longus 



N. ulnaris 



Fig 35. The motor points on the anterior surface of the forearm and 
hand. 



numerous sensory nerves. When the muscles or 
motor nerves are reached, the density is much 
reduced, and may not suffice for stimulation. 
Thus the result may be not motor stimulation, 
but simply pain from stimulation of the sensory 



STIMULATION OF MUSCLE AND NERVE 129 

nerves. For painless motor stimulation it is, 
therefore, necessary to increase the strength of 
the current which reaches the muscle or motor 
nerve and to diminish the density of the current 



M. inteross. dors. IV 
M. abd. digit, min. 




M. ext. pollicis longus 
M. ext. indicis propr. 



M. ext. indicis propr. 
M. ulnaris extern. 

M. rad. ext. brevis 



— M. ext. dig. min. propr. 

— M. ext. dig. communis 

M. supin. brevis 



M. rad. ext. longus - 
M. supin. longus ■ 



Fig. 36. The motor points on the posterior surface of the forearm and 
hand. 

at the electrodes. These ends are accomplished 
by using for electrodes large metal plates cov- 
ered with sponge or cotton wet with saline solu- 
tion. The liquid diminishes greatly the resistance 
of the epidermis, so that more current reaches 



130 GENERAL PROPERTIES OF LIVING TISSUES 

the deeper tissues ; and the large surface offers a 
broad path for the current, so that the current lines 
are not so concentrated as to stimulate painfully 
the sensory nerves of the cutis. One sponge elec- 
trode may be made considerably smaller than the 
other without forfeiting this advantage, while the 
smaller size makes it easier to localize the stimulus. 

Muscles are best stimulated through their 
nerves, for two reasons : the nerve responds to 
a weaker stimulus than the muscle; and, sec- 
ondly, it is much easier to secure contraction of 
the whole muscle by stimulating the nerve than 
by attempting to pass a current through the 
muscle directly. The smaller electrode should 
be placed over the nerve, the larger on some in- 
different region. The indifferent electrode may 
be placed over the muscle itself, if it is important 
that the resistance shall not be increased by the 
too great separation of the electrodes. 

Duchenne found that certain points were es- 
pecially favorable for the stimulation of indi- 
vidual muscles. Eemak discovered that these 
" motor points " were simply the places at which 
the nerves entered the muscle. The motor points 
of the forearm are shown in Figs. 35 and 36. 

Stimulation of Motor Points. — Arrange the 
inductorium for single induction shocks. De- 
termine by the electrolytic method which pole 



STIMULATION OF MUSCLE AND NERVE 131 

of the secondary coil is the cathode when the 
primary current is broken (page 158). To this 
pole connect the small (stimulating) electrode ; 
to the other pole connect the large (indifferent) 
electrode. Place the indifferent electrode on 
the arm or neck. With the small electrode 
make out the motor points indicated in Figs. 35 
and 36. 

Polar Stimulation of Human Nerves. — In the 
hands of the earlier observers the stimulation 
of nerves within the body gave results often 
contrary to the law of polar stimulation so easily 
demonstrated in extirpated nerves. The ex- 
planation of these inconstant results lay in the 
failure to comprehend the distinction between 
the stimulating positive and negative electrodes 
and the physiological anode and cathode (compare 
page 108). Even when the monopolar method 
is employed, and a small electrode is brought as 
near as possible to the nerve to be stimulated, 
while a large indifferent electrode is placed on 
some other part of the body, it is impossible to 
secure true monopolar stimulation. The current 
entering at the anode does not remain in the 
nerve, but very soon passes out into the sur- 
rounding tissues (Fig. 37). Hence there are 
physiological cathodes on both sides of the posi- 
tive electrode, and for the like reason physiologi- 



132 GENERAL PROPERTIES OF LIVING TISSUES 



CCCCCC AAAAAA 



cal anodes on both sides of the negative electrode. 
Thus both anodal and cathodal stimulation take 
place, whichever electrode rests over the nerve. 
It is therefore incorrect to speak of ascending 
and descending currents in the case of nerves 
stimulated in situ. It should be 
pointed out, too, that the density 
of the current is greater on the 
side of the nerve nearer the 

Fig. 37. 

electrode than on the more deeply 
placed side cut by current lines already rapidly 
diverging. 

With these facts in mind, we may compare 
the polar stimulation of human nerve with the 
law already determined for the isolated nerves 
of the frog (page 115). 

The Brass Electrodes. — The brass electrodes, 
used chiefly for the stimulation of human muscles 
and nerves, are two in number: 
an " indifferent " electrode, con- 
sisting of a brass plate, 3x6 
cm., with binding post, and 
a " stimulating " electrode, of 
brass rod, 6 cm. long, ringed 
at one end and provided at the 
Flg ' 38 ' other with a binding post. Be- 

tween these the rod is insulated with rubber tubing. 
The electrodes should be covered with cotton wet 



STIMULATION OF MUSCLE AND NERVE 133 

with normal saline solution. The larger electrode 
may be fastened upon the arm or other indifferent 
region, and the smaller may be used to stimulate the 
nerves or muscles, for example the abductor indicis, 
or to find the "motor points." 

Connect 8 dry cells in series (the carbon of 
one cell to the zinc of the next, etc.). Coupling 
in this way enables the electromotive force of 
each cell to be added with slight loss to that of 
the others, provided the resistance in the circuit 
outside the cells is so great that the internal 
resistance of the battery disappears in compari- 
son, as is the case where living tissues form part 
of the circuit. Connect the terminal zinc and 
carbon pole through a pole-changer (with cross- 
wires) to a small and a large electrode covered 
with cotton thoroughly wet with strong saline 
solution. Place the small electrode over the 
ulnar nerve between the internal condyle and 
the olecranon, a little above the furrow. Make 
and break the current. If no contraction is 
secured, add cells to the battery until contraction 
occurs. 

It will be found that the first contraction 
occurs on closure with the cathode over the 
nerve. With this strength of current the opening 
contraction will be absent. 

Turn the pole-changer so as to bring the anode 



134 GENERAL PROPERTIES OF LIVING TISSUES 

over the nerve, and increase the intensity still 
further. 

A strength will be reached at which closure 
with the anode over the nerve will cause contrac- 
tion, but the opening of the current will still be 
without effect. A slightly greater intensity will 
now bring out the anodal opening contraction. 1 

In the mean time the cathodal closing con- 
traction has increased in force with each addition 
to the intensity of the current. With about 18 
cells, the muscle twitch on closure may give 
place to a continued contraction or tetanus, the 
cathodal closing tetanus. Further increase gives 
cathodal opening contraction, and finally very 
strong currents sometimes cause anodal closing 
tetanus. Thus we have 

1. Cathodal closing contraction. 

2. Anodal closing contraction. 

3. Anodal opening contraction. 

4. Cathodal closing tetanus. 

5. Cathodal opening contraction. 

6. Anodal closing tetanus (rare). 
Sometimes the anodal opening precedes the 

anodal closing contraction. 

1 Sometimes anodal opening contraction precedes the closing 
contraction. This inconstancy results from variations in cur- 
rent strength clue to differences in the tissues surrounding the 



STIMULATION OF MUSCLE AND NERVE 135 

The apparent deviation from the law of polar 
excitation (cathodal on closure, anodal on open- 
ing) is explained by the presence of a physi- 
ological anode and cathode at each electrode, 
as already mentioned. The appearance of cath- 
odal closing contraction before anodal closing 
contraction is due to the fact that when the 
negative electrode lies over the nerve the physi- 
ological cathode will be found on the side of the 
nerve next the electrode. The nearer the elec- 
trode, the greater the current density, and hence 
the earlier the threshold value is reached. When, 
however, the positive electrode lies over the 
nerve, the physiological cathode will be found 
on the side of the nerve farther from the elec- 
trode, where the density is less, owing to the 
divergence of the current lines. The threshold 
value will be reached first at the point of higher 
density, and consequently the first contraction 
will appear while the negative electrode rests 
over the nerve. The anodal opening contraction 
appears before the cathodal opening contraction 
for a similar reason. 

Reaction of Degeneration. — Whenever a nerve 
is severed, the portion separated from the cell of 
origin of the nerve " degenerates." The degener- 
ation does not begin at the section and advance 
to the terminal branches, but takes place al- 



136 GENERAL PROPERTIES OF LIVING TISSUES 

most or quite simultaneously throughout the 
nerve. Eanvier states that it begins first in the 
end plates. Severed nerves in the brain and 
spinal cord degenerate in the same way, and this 
" Wallerian degeneration " (Waller, 1850) is a 
valuable aid in tracing the path of nerve fibres 
in the central nervous system. Degeneration is 
accompanied by changes in the reaction to the 
electric current which form a valuable aid in the 
diagnosis of the seat of the lesion in cases of 
paralysis. The muscle reacts imperfectly, or not 
at all, to the brief induction current, while its 
reaction to the long galvanic current may even 
be greater than usual. 

Expose each gastrocnemius muscle in a frog, 
the left sciatic nerve of which has been severed 
ten days before this experiment. Stimulate each 
muscle with weak induction currents and with 
the galvanic current. 

The muscle, the nerves of which are degen- 
erated, reacts more readily to the galvanic current 
than to the brief induction current. The normal 
muscle shows the opposite reaction. 

In man, the reaction of degeneration in the 
case of muscle consists of a lessened or lost 
excitability to the induced current with increased 
excitability to the galvanic current. The duration 
of contraction may be greater than normal. In 



STIMULATION OF MUSCLE AND NEEVE 137 

polar stimulation, anodal closing contraction may 
appear before cathodal closing contraction, — a 
reversal of the normal sequence. 

In degenerated nerve there is of course a total 
loss of irritability, corresponding to the destruc- 
tion of the axis-cylinder. 

Galvanotropism 

Paramecium. — Connect two non-polarizable 
electrodes through a pole-changer with a dry cell. 
On a glass microscope-slide make with wax an 
enclosure about one centimetre square and a few 
millimetres high. Place in this a little hay 
infusion containing Paramecia. Bring near the 
two opposite sides of the wax cell non-polarizable 
electrodes, provided with a thick thread that shall 
dip into the infusion. Examine the infusion with 
a very low power. Close the key. 

Upon closure each Paramecium turns the an- 
terior end of the body towards the cathode and 
swims in that direction. In a very short time 
the anodal region is free, and the Paramecia are 
gathered at the cathode, where they remain so 
long as the current flows. 

Change the direction of the current. 

The Paramecia now turn to the anode and 
swim in that direction, but the anodal grouping 
is less complete than the cathodal, and lasts but 



138 GENERAL PROPERTIES OF LIVING TISSUES 

a short time. Careful observation shows that 
in Paramecium the galvanic reaction consists in 
placing the long axis of the body in the current 
lines. The outermost individuals in the liquid 
will therefore describe a curve corresponding to 
the curved outer current lines. 

All protozoa and many other animals (for ex- 
ample, the tadpole and the crayfish) show gal- 
vanotropism, but in some, movement on closure 
is toward the positive pole (positive galvano- 
tropism). 

These experiments on skeletal, smooth, and 
cardiac muscle, on nerve, and on infusoria, sug- 
gest that polar excitation occurs wherever a gal- 
vanic current passes through irritable tissue. 
Further experience would confirm this view. We 
have seen that the changes at the cathode when 
the current is made are not momentary, as re- 
quired by the hypothesis of DuBois-Eeymond, 
but continue so long as the current flows. This 
fact appears still more clearly when the influence 
of the duration of the current is examined. 

Influence of Duration of Stimulus 

1. Smoke a drum. Arrange a muscle lever to 
write on the smoked paper. Prepare non-polariz- 
able electrodes and fasten them on the glass plate 




STIMULATION OF MUSCLE AND NERVE 139 

of the nerve holder. Arrange the inductorium 
for maximal induction currents. Lead from the 
secondary coil to a pair of the end cups of the 
pole-changer (without cross-wires), as in Fig. 39. 
To the opposite cups of the pole-changer bring 
wires from a dry cell. 
Connect the remaining 
cups with the non-polar- 
izable electrodes. Turn 
the rocker towards the in- 
duction coil. Fasten the 
pelvic attachment of the Fig. 39. 

curarized sartorius in 

the muscle clamp. Tie a thread to the fragment 
of tibia, and fasten the thread to the upright pin 
of the muscle lever, so that the horizontal muscle 
shall record its contraction on the drum. Start 
the drum at moderate speed. Eecord contrac- 
tions, (1) with maximal break shocks, (2) with 
closure of galvanic current. Compare the curves. 

The curve from galvanic stimulation will be of 
greater height and duration, and the summit of 
the curve will be less pointed, indicating that 
the muscle remains longer in the stage of ex- 
treme shortening. 

Other evidence that the duration of the stimu- 
lus modifies the character of the contraction is 
afforded by the following experiments : — 



140 GENERAL PROPERTIES OF LIVING TISSUES 

2. Make two cuts, 5 mm. apart, through the 
frog's stomach at right angles to the long axis. 
Hang the ring thus secured in the moist cham- 
ber. Pass a bent hook through the lower end of 
the ring, and attach it by means of a fine copper 
wire to the hook on the muscle lever. Carry the 
end of the copper wire to the binding post on the 
muscle lever. 

Stimulate not more than twice with single in- 
duction currents of a strength about the threshold 
value for skeletal muscle of frog. 

There will be no contraction. 

Stimulate with galvanic current (two dry cells), 1 
writing three curves, the duration of closure be- 
ing approximately one-fifth second, one, and five 
seconds, respectively. Compare the curves. 

The maximum shortening with currents of 
brief duration (1 second) is very much less than 
with currents of three or four seconds or over. 
The briefer the current also, the quicker will the 
maximum shortening be reached, and the quicker 
will be the relaxation. 

3. If the galvanic current is very rapidly made 
and broken, the muscle will not contract. 

1 If the muscle does not respond, wrap it with filter paper 
moistened with normal saline solution, and wait until the tonic 
contraction due to the cutting has passed off. The tonus ma} 7 
sometimes be lessened by passing a galvanic current through the 
preparation (p. 153); 



STIMULATION OF MUSCLE AND NERVE 141 

The same is true of the ureter (Engelmann). 

4. Tonic Contraction. — Examine the contrac- 
tion curve already recorded by the smooth 
muscle of the frog's stomach. Note that the 
muscle remains contracted during the passage 
of the current. The curves secured from the 
curarized sartorius (page 139) also show this, 
but to a much less degree ; the sartorius does 
not resume its former length after the twitch or 
closure of the galvanic current, but remains con- 
tracted to a slight extent. This tonic contrac- 
tion appears much more plainly in fatigued 
muscles. 

Fatigue a sartorius muscle by stimulating it 
with a galvanic current repeatedly made and 
broken. After a time, the twitch on closure will 
become very feeble, and finally will disappear, 
while the tonic shortening during the passage of 
the current is still very evident. 

5. The influence of duration is shown also in 
the opening contraction. 

Fasten the pelvic attachment of a sartorius 
muscle in the muscle clamp and connect the 
other end with the upright pin of the muscle 
lever, so that the horizontal muscle shall record 
its contraction on a drum. Place the non-polar- 
izable electrodes on the ends of the muscle. 
Allow the "galvanic current from a dry cell to 



142 GENERAL PROPERTIES OF LIVING TISSUES 

pass through the muscle until the closure tonic 
contraction has disappeared, then open the key. 
Neglect the opening twitch. 

The muscle will not return to its original 
length, but will remain contracted for a time 
(opening tonic contraction). 

Close the key again. 

The tonic contraction will disappear. 

The galvanic current in this case checks (in- 
hibits) a contraction. This new action is dis- 
cussed on page 153. 

6. Rhythmic Contraction. — That the galvanic 
current acts as a stimulus so long as it continues 
to flow is shown also by the fact that its passage 
through contractile tissue may cause the muscle 
to fall into rhythmic contractions. These are 
easy to produce in muscles which normally con- 
tract in rhythms, for example, the heart ; but 
they may under some circumstances be observed 
also in smooth muscle, and even in skeletal 
muscles. 

Connect a dry cell through a simple key with 
the metre posts of the rheochord. Join the non- 
polarizable electrodes to the positive post and the 
slider. Bring the slider against the positive post, 
so that no current shall flow through the elec- 
trodes when they are joined by the tissue. 

Expose the heart. With a sharp knife bisect 



STIMULATION OF MUSCLE AND NERVE 143 

the ventricle transversely. Rest this "apex" 
preparation between the tips of two non-polar- 
izable boot electrodes. Keep the tissue moistened 
with normal saline solution, but avoid excess. 
Close the key. Move the slider along the wire. 

When the current taken off reaches the thresh- 
old value, the apex will begin to beat rhyth- 
mically. Increasing the current strength will 
increase (within limits) the frequency of con- 
traction. 

Skeletal Muscle. — The curarized sartorius may 
sometimes be brought into rhythmic contraction 
by constant currents (Hering). If the irrita- 
bility of the muscle at the point of stimulation 
be increased by applying to the cathodal region 
a two per cent solution of sodium carbonate, the 
constant current will produce strong rhythmic 
contractions. 

Smoke a drum. Fasten the pelvic end of the 
sartorius in the muscle clamp, and attach the 
tibial end by a thread to the vertical pin on 
the muscle lever so that the horizontally extended 
muscle may write its contraction on a drum. 
Lay on the tibial fifth of the muscle a piece of 
filter paper, wet with two per cent solution of 
sodium carbonate. Connect a dry cell through 
a simple key with the metre posts of the rheo- 
chord. Connect the non-polarizable electrodes 



144 GENERAL PROPERTIES OF LIVING TISSUES 

with the positive post and the slider. Bring the 
slider near the positive post. When the sodium 
carbonate has acted for 15 minutes, bring the 
cathode against the tibial end, the anode against 
the pelvic end of the muscle. Close and open the 
circuit, moving the slider meanwhile to find 
the current which will give closing contraction. 
At this point keep the circuit closed. 

Bhythmical contractions usually appear. 

Periodic contractions are observed also in 
smooth muscle, stimulated with the constant 
current. Any form of constant stimulus will 
serve to produce them, pressure — as in the 
heart, bladder, and intestine — and chemical 
action, being especially noteworthy. 

Continuous Galvanic Stimulation of Nerve may- 
cause the Periodic Discharge of Nerve Impulses. — 
If two non-polarizable electrodes are allowed to 
rest on the muscle (horizontally suspended), and 
are connected to a capillary electrometer, the 
meniscus of which is projected through a slit 
onto rapidly moving sensitized paper, the shadow 
of the meniscus will make a straight line on the 
photographic paper so long as the muscle is at 
rest. When, however, the nerve of the muscle 
is stimulated with the galvanic current and 
closing tetanus appears, the straight line will be 
broken by 10-15 oscillations per second. These 



STIMULATION OF MUSCLE AND NERVE 145 

oscillations are produced by the difference of 
potential created by each contraction wave as it 
passes over the muscle (contracting muscle is 
negative towards muscle at rest, see page 302), 
and demonstrate that the tetanus is a fusion 
of individual contractions produced by successive 
stimuli. 

Hence, nerve, like muscle, responds to a contin- 
uous stimulus by a periodic discharge of energy. 

Ulnar Nerve. — Connect 15 dry cells in series 
(zinc to carbon), and join the last zinc and carbon 
through a key to a small brass stimulating 
electrode one cm. in diameter, and a large " in- 
different" electrode (brass plate 6.5 x 3.5 cm. 
covered with cotton wet in solution of common 
salt). Hold the indifferent electrode in the left 
hand, and apply the stimulating electrode to the 
ulnar nerve at the elbow. 

A peculiar tingling sensation will be felt so 
long as the current flows. 

Polarization Current. — Let the sciatic nerve 
rest on a pair of non-polarizable electrodes in 
the moist chamber. Connect the electrodes to 
the side cups of the pole-changer (without cross- 
wires). Connect one end pair of the pole-changer 
cups with a dry cell. Turn the rocker to the 
opposite side to prevent the battery current from 
reaching the electrodes until it is wanted. Con- 

10 



146 GENERAL PROPERTIES OF LIVING TISSUES 

nect the remaining pair of cups through a closed 
short-circuiting key with the capillary electrom- 
eter. Let the galvanic current flow some min- 
utes through the nerve, then turn the rocker 
towards the electrometer and open the short- 
circuiting key. 

Note a movement of the meniscus in a direction 
indicating that the former cathode is now posi- 
tive to the former anode. 
The nerve is polarized. 
Positive Va riation. — 
If the polarizing current 
is strong and brief, the 
negative polarization 
after-current will speed- 
ily give place to a positive current, i. e. one in the 
direction of the polarizing current. This positive 
current is really an action current. When the 
polarizing current is broken, the rise of irritabil- 
ity at the anode stimulates points nearer the 
anode more strongly than points farther away. 
Points nearer the anode become, therefore, nega- 
tive to points farther away, and a current flows 
through the electrometer circuit from the less 
negative to the more negative pole, and through 
the nerve in the direction from anode to cath- 
ode. This positive variation is seen only in 
living nerves. 




Fig. 40. 



STIMULATION OF MUSCLE AND NERVE 147 

Polar Fatigue. — Connect non-polarizable elec- 
trodes through a simple key with a dry cell. 
Fatigue a sartorious muscle by opening and clos- 
ing the galvanic circuit (leave a brief interval 
between opening and closure). Closure will at 
length be followed by no contraction. Arrange 
an inductoriurn for single induction currents (the 
pole-changer may be placed in the primary cir- 
cuit as a simple key). Test now the irritability 
of the muscle by stimulating it with single induc- 
tion currents. 

The muscle will be irritable except in the cath- 
odal region. The fatigue has been local (polar). 

Opening and Closing Tetanus. — 1. Arrange a 
moist chamber with a muscle lever to write on a 
smoked drum. Place two non-polarizable elec- 
trodes in the moist chamber and connect them 
through a pole- changer with a dry cell. Make a 
nerve muscle preparation from a frog that has 
just been brought from a cold room into the warm 
laboratory. Secure the femur in the femur clamp 
of the moist chamber. Let the nerve rest on the 
non-polarizable electrodes. Attach the muscle 
to the lever. Bring the writing point against the 
slowly moving drum. Close the key. 

If the frog has been well cooled (below 10° C), 
the muscle will fall into tetanus both on closing 
and on opening the circuit. Note that the curve 



148 GENERAL PROPERTIES OF LIVING TISSUES 

is quite regular. If tetanus fails to appear, paint 
the cathodal region with one per cent solution of 
sodic carbonate, thus raising the irritability, and 
repeat the experiment. The curve secured in 
this way is likely to be irregular. 

Produce opening tetanus, and while the muscle 
is contracting close the current again. 

The tetanus will disappear ; the irritability 
will be reduced in the anodal region, from the 
polarization of which the tetanus was produced. 

Open the current again. When the tetanus 
reappears reverse the pole-changer and close the 
current. 

The tetanus will be increased ; the irritability 
in the former anodal region will suffer a catelec- 
trotonic increase. 

2. A beautiful demonstration of polar excitation 
may be made in this experiment. Connect the 
electrodes in such a way that the intrapolar cur- 
rent shall be. descending (i.e. towards the muscle). 
When the opening tetanus appears, cut away 
the anode by severing the nerve between the 
electrodes. 

The contraction ceases with the removal of the 
source of stimulation. 

3. The stimulating effect of the salts of the 
alkalies has been explained by their attraction 
for water, the loss of which increases the effect 



STIMULATION OF MUSCLE AND NERVE 149 

of the galvanic current on nerve. When the 
irritability of the nerve is raised by drying, weak 
currents may give opening contractions, although 
they are absent in normal, uninjured nerves. 
The interval between the opening of the current 
and the resulting contraction is then markedly 
long. In nerves in the first stage of drying the 
intensity of the nerve impulse (height of con- 
traction of attached muscle) is also more than 
usually dependent on the duration of the 
current. 

4. The opening tetanus (so-called Bitter's tet- 
anus) is probably caused by the rise of irritabil- 
ity, which takes place in the anodal region when 
the current is shut off, acting on a nerve already 
in latent excitation. A similar condition can be 
produced as follows : — 

Smoke a drum. Connect a dry cell through an 
open key and an electro-magnetic signal with the 
metre posts of the rheochord (Fig. 41). Connect 
the zero post and the slider of the rheochord with 
the pole-changer (with cross-wires), and the latter 
with two non-polarizable electrodes placed in the 
moist chamber. Make a nerve-muscle prepara- 
tion, and secure the femur in the femur clamp 
of the moist chamber. Attach the muscle to the 
muscle lever. Bring the writing points of the 
muscle lever and the electro-magnetic signal 



150 GENERAL PROPERTIES OF LIVING TISSUES 

against the smoked surface in the same vertical 
line. Let the nerve rest on the non-polarizable 
electrodes. In the remaining two posts in the 
moist chamber fasten stimulating electrodes. 
Connect the latter to the inductorium, arranged 
for tetanizing currents, short-circuiting key closed. 
Bring the stimulating electrodes against the nerve 
between the non-polarizable electrodes and the 




Fig. 41. 

muscle. Let the secondary coil be at such a dis- 
tance that the tetanizing current will be just 
below the threshold value. Turn the pole-changer 
so that the anode shall be next the tetanizing 
electrodes. Make and break the galvanic current, 
recording the contraction on a slowly moving 
drum. Now open the short-circuiting key, and 
after half a minute, and while the sub-minimal 
tetanizing current is still passing through the 



STIMULATION OF MUSCLE AND NEEYE 151 

nerve, make and break the galvanic current 
again. 

A moderately strong galvanic current will now 
produce an opening tetanus (anodal stimulation 
of a region the irritability of which has been 
raised by the sub-minimal tetanizing current). 
Other effects are a lengthening of the latent 
period, and an increased dependence on the 
duration of the galvanic current (see page 138). 

Eeverse the pole-changer, so that the tetanizing 
electrodes fall in the cathodal region. Repeat 
the experiment, comparing the results of cathodal 
stimulation without and with the sub-minimal 
tetanizing current. 

With sub- minimal tetanization, an increase in 
the height of the closing contraction, when the 
galvanic current is not too strong, will be seen ; 
when the galvanic current is stronger, closing 
tetanus will also be observed. 

Polar Excitation in Injured Muscle. — Smoke a 
drum. Make non-polarizable electrodes. Con- 
nect a dry cell through a simple key and 
pole-changer (with cross-wires) with the non- 
polarizable electrodes. Prepare a sartorius mus- 
cle with bony attachments. Fasten the pelvic end 
in the muscle clamp. Tie a thread to the tibial 
end, and fasten the thread to the upright pin of 
the muscle lever, so that the muscle is extended 



152 GENERAL PROPERTIES OF LIVING TISSUES 

horizontally. Bring the writing point against the 
drum. Light a Bunsen burner. Heat a wire, 
and kill the pelvic end of the muscle by laying 
the hot wire against it. Bring one non-polar- 
izable electrode upon each end of the muscle. 
Arrange the pole-changer so that the cathode 
shall be at the pelvic end, and the current there- 
fore " atterminal," i. e. directed toward the 
"thermal cross-section." Close the simple key. 

No contraction, or a very slight contraction, 
will be seen. 

Open the key. Reverse the pole-changer, so 
that the current shall be " ab terminal." Close 
the simple key. 

The ordinary closing contraction will be seen. 

The great difference here shown between the 
polar excitability in the uninjured and injured 
region is probably due to chemical changes in 
the injured part. Similar results can be obtained 
by painting the end of the muscle with one per 
cent solution of acid potassium phosphate. The 
irritability is lessened by this salt, but returns to 
normal if the altered end of the muscle is bathed 
in 0.6 per cent sodium chloride solution. 

Sodium carbonate has an effect opposite to that 
of the potassium salts. 

Wet the pelvic end of a fresh muscle with one 
per cent solution of sodic carbonate. After a 



STIMULATION OF MUSCLE AND NERVE 153 

short time, test the irritability to weak, ascend- 
ing (i. e. cathode at pelvic end) currents. 

The closure of ascending currents will give 
extraordinarily large contractions. 

The cause of this change in irritability is not 
the presence of dead contractile tissue, for elec- 
trodes can be wrapped in dead muscle and used 
to stimulate normal muscle without loss of irri- 
tability being noticeable. 

When the end of the fibre is killed, the patho- 
logical change passes gradually through the 
whole of the fibre. 



Polar Inhibition by the Galvanic Current 

It remains now to consider the inhibitory 
action of the galvanic current, to which attention 
was called on page 142. 

Heart. — Connect a dry cell through a simple 
key with the and 1 metre posts of the rheochord. 
Connect non-polarizable electrodes through a pole- 
changer with cross-wires (Fig. 30), with the slider 
and the positive post of the rheochord. Pith the 
brain, not the cord, of a frog, and place the animal, 
back down, in the holder (Fig. 29, page 112), and 
expose the heart, without unnecessary loss of 
blood, according to the method described on page 
112. Open the delicate membrane (pericardium) 



154 GENERAL PROPERTIES OF LIVING TISSUES 

which surrounds the heart. Let one electrode 
rest on the larynx. Lay upon the tip of the 
other electrode a strand of lamp wick or absor- 
bent cotton wet with normal saline solution. 
Bring this electrode over the heart so that the 
free end of the strand rests on the ventricle and 
moves with it. Turn the pole-changer to make 
this electrode the anode. Make the current. 

At each systole, the portion of the ventricle 
immediately about the anode will not contract 
with the rest, but will remain relaxed (local dias- 
tole). Thus while the greater part of the ven- 
tricle becomes pale as the blood is squeezed out 
of its wall by the contraction, the anodal region 
remains dark red. From this region the relaxa- 
tion spreads over the rest of the ventricle. Ee- 
verse the pole-changer. Break the current. 

The cardiac electrode is now the cathode. In 
the systole following the breaking of the current, 
the cathodal region will remain relaxed during 
contraction of the ventricle. 

This experiment demonstrates that the galvanic 
current not only may stimulate, but may check 
or inhibit contraction. In the former case, the 
conversion of potential into active energy is set 
going; in the latter, it is prevented. Inhibi- 
tion plays a large part in the physiology of the 
day. 



STIMULATION OF MUSCLE AND NERVE 155 

Polar Inhibition in Veratrinized Muscle. — A 

similar inhibitory effect can be demonstrated in 
skeletal muscle previously placed in continued 
("tonic") contraction by veratrine poisoning. 
Inject with a fine glass pipette seven drops of 
one per cent solution of veratrine acetate in the 
dorsal lymph sac of a frog. 

Arrange two muscle levers to write on a drum. 
Between them place an electromagnetic signal. 
Let all three writing points be in the same vertical 
line. Connect a dry cell through a simple key 
with an inductorium arranged for single induc- 
tion shocks. Connect non-polarizable electrodes 
through another simple key and the electro- 
magnetic signal with a dry cell. Prepare a 
sartorius muscle with pelvic and tibial attach- 
ments. Fasten the muscle about the middle in 
the cork clamp. Fasten the cork clamp verti- 
cally in the jaws of the muscle clamp. Carry 
threads from each end of the muscle to one of 
the muscle levers. Place the non-polarizable 
electrodes near the respective ends of the mus- 
cle. Note which is the anode. Bring wires 
from the secondary coil of the inductorium to 
the ends of the muscle. Start the drum mov- 
ing slowly. Stimulate the muscle with a single 
induction shock. There will be a prolonged con- 
traction, characteristic of veratrine poisoning. So 



156 GENERAL PROPERTIES OF LIVING TISSUES 

soon as this contraction is well under way, make 
the constant current. 

The anodal half of the muscle will show a dis- 
tinct relaxation ; the cathodal half will not relax, 
but may even contract a little more. 

Stimulation affected by the Form of the 
Muscle 

Connect a dry cell through a simple key to 
the metre posts of the rheochord. Bring wires 
from the non-polarizable electrodes to the positive 
post and the slider, interposing the pole-changer 
with cross-wires so that the direction of the cur- 
rent can be changed. Place the slider against 
the positive post, so that all the current passes 
back to the cell. 

Prepare a curarized sartorius muscle with its 
bony attachments. Fasten the pelvic fragment 
in the muscle clamp. Tie a thread about the 
tibia and fasten the thread to the upright pin of 
the muscle lever. Let the cathode rest on the 
tibial end of the muscle, the anode on the pelvic 
end ; the current will then be descending. Move 
the slider a few centimetres away from the posi- 
tive post, and make the current. If no contrac- 
tion follows, move the slider farther along, and 
make the current again. 

With careful work, it will be shown that with 



STIMULATION OF MUSCLE AND NERVE 157 

descending currents, the first contraction will 
be on closure only. With ascending currents, 
the first contraction will be on opening the 
current. 

The explanation is that, with currents which 
pass through the sartorius from end to end 
the point of greatest density is the smaller, 
lower end. This is cathodal in descending 
currents, anodal in ascending currents. 

Effect of the Angle at which the Current 
Lines cut the Muscle Fibres 

Connect non-polarizable electrodes through 
a key with a dry cell. Build on a glass plate 
with normal saline clay two parallel walls a 
little longer than the sartorius muscle and 
one centimetre apart. Join the ends with 
wax, to make a rectangular trough. Eemove 
a sartorius muscle from a curarized frog, 
avoiding all injury to the muscle. Place the 
muscle in the trough, and cover it with normal 
saline solution. Bring a non-polarizable elec- 
trode against the centre of each long side, so 
that the current lines shall cut the muscle 
fibres at right angles. Close the key. 

There will be no contraction. The muscle is 
inexcitable to currents that cross its fibres at 
right angles. 



158 GENERAL PROPERTIES OF LIVING TISSUES 

Alter the angle by moving one electrode to 
the right, the other to the left, and repeat the 
experiment. 

The stimulating effect will increase as the 
angle between current lines and the long axis of 
muscular fibres diminishes. 

Nerves also are inexcitable to transverse cur- 
rents. Differences in resistance play a great 
part here. The resistance of nerves is said to 
be 2J million times that of mercury, when the 
current passes along the nerve, and 12 J million 
times when it passes transversely. 



The Induced Current 

The break induction current, owing to its rapid 
rise from zero to maximum intensity, is a more 
effective physiological stimulus than the make 
current, and may 'therefore be chosen for 
experimentation. 

1. The direction of the induction current in 
the secondary coil is most easily determined 
electrolytically. 

Arrange the inductorium for maximal currents. 
Bring wires from the posts on the secondary coil 
to a piece of filter paper wet with starch paste 
containing iodide of potassium. Exclude the 
make currents with the short-circuiting key ; 



STIMULATION OF MUSCLE AND NERVE 159 

pass the maximal break currents through the 
electrolyte. 

Iodine will be set free at the anode and will 
combine with the starch to form blue iodide of 
starch. 

Mark the positive post on the secondary coil 
with a plus sign. 

2. Connect the poles of the secondary - coil 
through a pole-changer with non-polarizable 
electrodes. Make a nerve-muscle preparation. 
Tie a ligature about the nerve about two cen- 
timetres from the central end. Place one elec- 
trode on each side of the ligature. The passage 
of a nerve impulse from the central electrode 
to the muscle will be prevented by the lig- 
ature, although the electric current can still 
pass between the electrodes. Turn the pole- 
changer so that the electrode on the periph- 
eral (muscle) side of the ligature shall be first 
the anode and then the cathode, and test the 
irritability to weak induction currents, begin- 
ning with the secondary coil some distance from 
the primary, and gradually increasing the intensity. 

Only cathodal stimulation will produce con- 
traction. The same result can be secured by 
separating the cathode and anode with ammonia. 
If the nerve is painted with ammonia in the 
intrapolar region, break currents cease to cause 



160 GENERAL PROPERTIES OF LIVING TISSUES 

contraction when the cathode is on the central 
side of the painted zone. Painting the cathodal 
region directly also prevents excitation. 

The failure of the induction current to stimu- 
late at the anode, on opening the current, is due 
to the exceedingly brief duration of the induced 
current ; there is not time for a sufficient anelec- 
trotonic alteration in excitability. If the current 
is shortened still more (if it be less than 0.0015 
sec), the cathodal excitation also disappears. 
With very strong currents, however, opening the 
current stimulates as well as closure. 

3. Additional evidence of polar action is 
secured by connecting the electrodes with the 
capillary electrometer through a closed short- 
circuiting key. The meniscus is brought into 
the field, the nerve is stimulated repeatedly 
with maximal break currents, and then stimu- 
lation is stopped, and the short-circuiting key 
in the electrometer circuit opened. The menis- 
cus will move in a direction indicating a higher 
potential at the anode (positive anodal polariza- 
tion current). 

4. Finally, it may be added that the galvanic 
current may increase the stimulating effect of the 
induced current as pointed out on page 80, but only 
when the cathode of the induced current falls in 
the cathodal region of the polarizing current. 



STIMULATION OF MUSCLE AND NERVE 161 

The law of polar excitation holds good then 
for the induced as well as the galvanic current. 
In fact, there is no essential difference between 
the physiological effects of induced currents and 
very brief galvanic currents. 

Increasing the intensity of the induced cur- 
rent increases at first the excitation (height of 
contraction). At length, however, with ascend- 
ing currents, a point is reached beyond which 
further increase in strength is followed first by 
the diminution and at length by the disappear 
ance of contraction. With still higher intensi- 
ties, the contractions reappear. This gap in the 
contraction series is explained by the increasing 
depression of irritability at the anode blocking 
the cathodal impulse ; when the intensity is still 
further increased, the opening of the current acts 
as a stimulus. A similar result may be secured 
with the galvanic current. 

Apparatus 

Normal saline. Bowl. Pipette. Towel. Simple key. 
Non-polarizable electrodes. Nerve holder. Potter's clay 
mixed with 0.6 per cent solution of sodium chloride. 
Saturated solution of zinc sulphate. Muscle clamp. 
Stand. 13 wires. Kymograph. Glazed paper. Two 
muscle levers. Thread. Kheochord. Two dry cells. 
Moist chamber. Glass plate. Ice. Paraffin paper. Cork 
clamp. Pole-changer. Beaker. Tripod, Sodium chloride. 
11 



162 GENERAL PEOPERTIES OF LIVING TISSUES 

Inductorium. Electrodes. Bunsen burner. Intestine of 
a rabbit. Electromagnetic signal. Tuning fork. Brass 
electrodes. Fine copper wire. Frog board. 2 pairs of 
metal electrodes, each passed through cork. Electrom- 
eter. Paramecia. Microscope. Glass slide. Bent hooks. 
One per cent solution of veratrine acetate. Fine glass 
pipette. Filter paper saturated with starch paste con- 
taining potassium iodide. Frogs. Fine rubber tubing 
for insulating electrodes. Ammonia. One per cent solu- 
tion of acid potassium phosphate. Two per cent solution 
of sodic carbonate. Ligatures. Filter paper. 



CHEMICAL AND MECHANICAL STIMULATION 163 



CHEMICAL AND MECHANICAL STIMULATION 

Chemical Stimulation 

The contractility, heat production, and other 
phenomena of the life of muscle rest at base on 
chemical processes. Anything that sufficiently 
alters these processes may be a stimulus. A most 
important source of stimulation is the alteration 
of the chemical composition of muscle through 
osmosis. 

Effect of Distilled Water. — PlaCe a sartorius 
muscle in distilled water. 

Irregular contractions usually occur. The 
muscle soon swells, and becomes white, turbid, 
cadaveric. 

These striking changes depend on the with- 
drawal of certain bodies by osmosis. Muscle 
contains large quantities of proteid, particularly 
proteids of the globulin class ; certain carbo- 
hydrates, such as glycogen ; nitrogenous and 
other extractives ; water ; and a number of in- 
organic salts. Most of these bodies are largely 
or wholly insoluble in water, and require for 
their solution the presence of inorganic salts. 



164 GENERAL PROPERTIES OF LIVING TISSUES 

The globulins, for example, are insoluble in dis- 
tilled water, but soluble in dilute solutions of 
sodium chloride. The osmosis of salts into the 
distilled water in the above experiment first 
stimulates and then destroys the contractility 
of the muscle. 

An increase in the saline content of the muscle 
juice or " plasma " also acts as a stimulus, and, if 
excessive, may be fatal. 

Strong Saline Solutions. — Place a sartorius 
muscle on a slightly inclined glass plate. Cover 
the lowest fourth of the muscle with crystals of 
sodium chloride. 

Irregular contractions will appear. 

Drying. — The effect of loss of water is best 
shown in nerve. 

Let the nerve of a nerve-muscle preparation 
dry. Note the twitching of the muscle as the 
water content diminishes. Test the irritability 
of the nerve from time to time with induction 
currents. It will first increase, then disappear 
as the nerve dries. 

Wet the nerve with 0.6 per cent sodium 
chloride solution. 

The irritability will reappear. 

To keep muscles and nerves in good condition 
for experimentation, it is necessary to moisten 
them with a solution containing the inorganic 
salts most abundant in the tissue-liquids in the 



CHEMICAL AND MECHANICAL STIMULATION 165 

proportions in which they are present in those 
liquids. Practically, a 0.6 per cent solution of 
sodium chloride has commonly been employed, 
in the case of the frog. Such a solution is said 
to be isotonic, i. e. neither giving nor taking 
water from the tissue. That it is not perfectly 
indifferent appears from this experiment. 

"Normal Saline." — Allow a sartorius muscle 
to stand half an hour in normal saline solution 
(0.6 per cent NaCl). Eecord its contraction in 
response to a maximal break induction current. 
In place of a simple twitch, a prolonged contrac- 
tion of abnormal height and duration will usually 
be secured. 

Importance of Calcium. — Place the " normal 
saline " sartorius in 0.6 per cent sodium chloride 
solution containing 10 per cent of saturated solu- 
tion of calcium sulphate. After ten minutes 
record the maximal break contraction. 

The abnormal contraction will have disap- 
peared. 

Constant Chemical Stimulation may cause Peri- 
odic Contraction. — Place a sartorius muscle in a 
solution of 5 grams NaCl, 2 grams Na 2 HP0 4 , and 
0.4 gram ISTagCOg in one litre of distilled water. 

Usually rhythmic contractions are seen. All 
contractile substance shows a tendency to peri- 
odic contractions in response to a constant stimu- 



166 GENERAL PROPERTIES OF LIVING TISSUES 

lus, whether chemical, mechanical, or electrical. 
There are reasons for believing that the rhythmi- 
cal contractions of the heart are the consequence 
of a constant chemical stimulus. 

Mechanical Stimulation 

Stimulate a nerve mechanically by pinching 
the cut end with forceps. 

No change will be seen in the nerve, but the 
muscle will shorten, and then relax. 

Mechanical stimulation has the advantage that 
it can be localized accurately, and for this reason 
it has been used where electrical stimulation 
seemed inapplicable. Tetanomotors have been 
constructed by Heidenhain and others to give a 
rapid succession of slight blows upon the nerve. 

Sudden pressure on a muscle or sudden exten- 
sion may cause contraction. Sometimes the 
whole muscle contracts, sometimes only the 
portion directly stimulated. 

Idio-Muscular Contraction. — With the point 
of the seeker stroke the diaphragm and other 
muscles of a recently killed rat, or other small 
warm-blooded animal, in a direction at right 
angles to the course of the fibres. 

A wheal, i. e. a long-continued shortening and 
thickening of the fibre stimulated, will be seen. 
If the animal be not too long dead, a momentary 



CHEMICAL AND MECHANICAL STIMULATION 167 

twitch of the whole of the fibre stimulated will 
precede the continued local contraction or wheal. 
The same phenomenon is seen for a briefer 
time on sharp mechanical stimulation of muscles 
in living animals, for example, the wheals raised 
by the blow of a whip. In men long ill of wast- 
ing diseases, e. g. phthisis, the idio-muscular con- 
tractions appear on drawing a pencil point across 
the muscles. Direct total stimulation of frog's 
muscle, especially in the spring months, may be 
followed by long continued contraction. Fatigue, 
cold, and many poisons, such as veratrine, favor 
the prolongation of the phase of shortening. The 
idio-muscular contraction is not a " tetanus," 
i. e. not a prolonged shortening due to successive 
contractions, the interval between which is too 
short to permit of relaxation, but a prolonged 
single contraction, the cause of which lies in the 
muscle and not in the nerve. 

Apparatus 

Normal saline. Bowl. Pipette. Towel. Glass plate. 
Distilled water. Sodium chloride. Solution of sodium 
chloride (0.6 per cent), containing 10 per cent of saturated 
solution of calcium sulphate. Solution containing 5 grams 
sodium chloride, 2 grams di-sodium hydrogen phosphate, 
and 0.4 gram sodium carbonate, in 1000 c.c. water. Small 
warm-blooded animal recently killed. Introduction coil. 
Dry cell. Key. Electrodes. 3 Wires. Frogs. 



168 GENERAL PROPERTIES OF LIVING TISSUES 



VI 

IRRITABILITY AND CONDUCTIVITY 

Irritability is the power of discharging energy 
on stimulation. The form in which the kinetic 
energy of muscle appears is partly mechanical 
work (the visible contraction) and partly molec- 
ular, — heat, chemical action, and electricity. 
In the nerve, the kinetic energy is wholly molec- 
ular ; an electromotive force is generated, prob- 
ably heat is set free (though this statement — 
which is based simply on analogy — is frequently 
disputed), and a molecular change — the nerve 
impulse — arises at the seat of stimulation. In 
both muscle and nerve, by virtue of their con- 
ductivity, the change induced by stimulation is 
as a rule not limited to the region stimulated, but 
passes in both directions along each stimulated 
fibre. In neither muscle nor nerve can the 
changes in energy spread transversely ; they are 
limited to the muscle- or nerve-fibre in which 
they arise. 

It will be shown that conductivity and irrita- 
bility are essentially different functions. 



IRRITABILITY AND CONDUCTIVITY 169 

The Independent Irritability of Muscle. — The 

stimulus that causes the contraction of a muscle 
may be applied either to the nerve or to the 
muscle itself. If to the nerve, the muscle will 
be thrown into the active state not by the origi- 
nal stimulus, but by a nerve impulse. If to the 
muscle, the nerve will still be stimulated, for 
examination shows terminal fibres distributed, in 
skeletal muscle at least, probably to every fibre, 
and with few exceptions to all parts of the 
muscle. The fact that muscles may contract 
when an electric current flows through them, or 
when otherwise stimulated, does not therefore of 
itself indicate that electricity is a stimulus to 
muscle protoplasm. Before this can be estab- 
lished, it will be necessary to demonstrate con- 
traction in parts of muscle not provided with 
nerves ; for example, the distal part of the sar- 
torius, or in muscles in which the nerves have 
been destroyed by curare or by degeneration. 

Nerve-free Muscle. — Remove the sartorius 
muscle, together with the portion of the pelvis 
and the tibia to which the muscle is attached, 
and lay it on a glass plate. Stimulate the distal 
(tibial) fifth, in which examination with the 
microscope would show the absence of nerve 
fibres, with a strong break induction current. 

The nerve-free muscle will contract. 



170 GENERAL PROPERTIES OF LIVING TISSUES 

Muscle with Nerves Degenerated. — A nerve 
fibre severed from its cell of origin dies or " de- 
generates " down to its ultimate endings. Expose 
the sciatic nerve in the middle of the thigh of a 
frog in which the nerve has been severed near 
the pelvis ten days before, so that the whole of 
the nerve distal to the section shall have degen- 
erated. Stimulate the degenerated trunk. 

No contraction is seen in the muscles of the 
leg. Stimulate the muscles directly. 

Contraction takes place. 

The Nerve-free Embryo Heart. — Embryological 
studies show that the nerves of the heart are 
formed from epiblast in the walls of the neural 
canal, and do not grow into the heart until the 
close of the third day of incubation (chick). 
The heart, however, begins to beat during the 
second day of embryonic life, before even the 
blood which it shall pump is formed. Thus 
the heart muscle, in the embryo, is capable of 
contraction in the absence of nerves. 

Cover an egg which has been incubated 60-70 
hours with 0.75 per cent solution of sodium 
chloride warmed to 38° C. Eemove the shell 
with the forceps over one third of the egg, be- 
ginning at the broad end, and leaving the shell 
membrane behind. Now remove the shell mem- 
brane. Note the beating heart. 



IRRITABILITY AND CONDUCTIVITY 171 

Paralysis of Nerve Endings with Curare. — 
Make two nerve muscle preparations A and B, 
and fill two watch glasses with curare solution. 
In one watch glass lay the nerve trunk of prep- 
aration A and in the other watch glass the muscle 
of preparation B. Cover muscle A and nerve B 
with filter paper moistened with normal saline 
solution, to prevent drying. At intervals of ten 
minutes stimulate nerve B with induction 
currents. 

When the poison has acted the stimulation of 
nerve B will produce no contraction of the at- 
tached muscle, which lies in the curare. Either 
the muscle or the nerve has been poisoned. 

Stimulate muscle B directly. 

It contracts. Hence the curare has poisoned 
the nerve ; probably the terminals of the nerve 
within the muscle. 

Now remove nerve A from the curare and 
stimulate the trunk of the nerve. 

The attached muscle will contract. Hence 
the trunk of the nerve has not been poisoned 
by the curare. 

It follows that curare poisons the endings of 
the nerve within the muscle. Therefore, the 
contraction of muscle B, in which the nerve end- 
ings were paralyzed, must have been due to the 
independent irritability of the muscle fibres. 



172 GENERAL PROPERTIES OF LIVING TISSUES 

The occurrence of idio-muscular contraction 
(see page 166) is an additional proof of the 
independent irritability of muscle. 

Irritability and Conductivity are Separate Prop- 
erties of Nerve. — 1. Carbon-dioxide. — Arrange 
the inductorium for tetanizing currents. Connect 
the secondary coil with the main posts of the 
pole-changer (cross-wires out). Connect the 




Fig. 42. The gas chamber, with bottle for generating carbon dioxide, 
and a pole-changer arranged to stimulate the nerve either within or without 
the chamber. The holes in the glass through which the nerve passes are 
plugged with normal saline clay. 

two other pairs of posts with the usual stimula- 
tion electrodes and the electrodes of the small 
gas chamber (Fig. 42). Join the inflow tube of 
the gas chamber with the outflow tube of the 
carbon-dioxide bottle. The gas chamber should 
rest on a glass plate. Make a nerve-muscle 
preparation, preserving the full length of the 
sciatic nerve up to the vertebral column. Tie 



IRRITABILITY AND CONDUCTIVITY 173 

a silk thread to the extreme end of the nerve, 
and fasten the thread to the end of the seeker 
by a drop of wax cement. With the aid of the 
seeker, pass the thread through the holes, and 
draw the nerve after, so that the nerve lies on 
the electrodes. The nerve should be drawn 
through until the muscle is close to the gas 
chamber. Stop the holes through which the 
nerve passes with normal saline clay. Bring the 
outer pair of electrodes against the central end 
of the nerve near its exit from the gas chamber. 
Determine which position of the pole-changer 
corresponds to each pair of electrodes. Stimulate 
the nerve first within the chamber, and then on 
the central end of the nerve, using a current just 
sufficient to cause tetanus. In both cases tetanus 
will result. Now pour 20 per cent hydrochloric 
acid on the marble in the generator. After the 
gas has passed through the chamber for a moment, 
stimulate as before. 

Stimulation of the portion of the nerve exposed 
to the carbon-dioxide is no longer effective, while 
stimulation of the part central to the gas chamber 
still produces tetanus. 

But the nerve impulses created by stimulation 
of the nerve central to the gas chamber cannot 
reach the muscle except by passing along the 
nerve and through the carbon-dioxide. The con- 



174 GENERAL PROPERTIES OF LIVING TISSUES 

ductivity of the nerve therefore is still sufficient, 
while the irritability has been suspended by the 
action of the gas. Hence, conductivity and irri- 
tability are by no means interchangeable terms. 

Their essential difference is further shown by 
the effect of alcohol vapor, which impairs con- 
ductivity while irritability is little changed. 

2. Alcohol. — Disconnect the rubber tube from 
the gas generator, and blow through the gas 
chamber until the carbon-dioxide is driven out. 
The nerve will recover its irritability. Deter- 
mine this by stimulating from time to time. 
When the nerve has recovered, drop a little 
alcohol through the long glass tube of the gas 
chamber, being careful that only the vapor of 
the alcohol comes into contact with the nerve. 
Stimulate both within and central to the chamber. 

After a time, tetanus will no longer be pro- 
duced by stimulating central to the chamber. 
Stimulation within the latter is still effective. 
Thus conductivity is impaired, while irritability 
remains intact, or at least is affected to a less 
extent. (The electrodes within the alcohol at- 
mosphere should not be too far from the opening 
through which the nerve passes to the muscle, 
else the loss of conductivity in this part of the 
nerve may make difficult the demonstration of 
irritability.) 



IRRITABILITY AND CONDUCTIVITY 175 

Minimal and Maximal Stimuli ; Threshold Value. 

— Arrange the gastrocnemius muscle to write on 
a smoked drum. Connect one binding post of 
the secondary coil to the muscle clamp, the 
other binding post to the post on the muscle 
lever. Load the muscle with 10 grams. De- 
scribe an abscissa on the smoked paper, turning 
the drum by hand. Send a feeble break induc- 
tion current through the muscle. 

There will be no response. 

Repeat the break currents, gradually moving 
the secondary closer to the primary coil. 

At a certain point the muscle will just con- 
tract (" threshold value "). This is a minimal 
contraction produced by a minimal stimulation. 

Turn the drum 5 mm., move the secondary 
coil 5 mm. nearer the primary, send in another 
break current, and record the contraction. Con- 
tinue this. 

The contraction in answer to each break cur- 
rent increases with the strength of the currents 
at first rapidly, then slowly, up to a certain point. 
Further increase in the strength of the stimulus 
produces no further increase of contraction. The 
stimulus and the resulting contraction have now 
become maximal. 

There is a striking disproportion between the 
energy of the stimulus necessary to throw a 



176 GENERAL PROPERTIES OF LIVING TISSUES 

nerve or muscle into the active state, and the 
energy that the stimulus sets free. It is as if a 
spark fell into powder; the active process is to 
be regarded, with some reservations, as an explo- 
sion. But only a part of the latent energy of 
muscle can be set free by any one stimulus. 

Threshold Value Independent of Load. — Re- 
peat the preceding experiment, and load the 
muscle with 50 grams instead of 10. 

The threshold value will not be changed. 
Summation of Inadequate Single Stimuli. — 
Place the secondary coil of the inductorium at 
such a distance from the primary that a break 
current shall be nearly, but not quite sufficient 
to cause a contraction. Let the muscle rest 
without stimulation for about a minute. Repeat 
the inadequate single stimulation at intervals of 
five seconds. No curve need be written. 
After a time, contraction will be secured. 
The excitation outlasts the stimulus, and rein- 
forces subsequent stimuli : finally, the summed 
excitations call forth a contraction. Summation 
is of frequent occurrence probably in all living 
tissues- 
Relative Excitability of Flexor and Extensor 
Nerve Fibres ; Ritter-Rollett Phenomenon. — Ex- 
pose the sciatic nerve in a brainless frog in 
the pelvic region. Set the hammer of the in- 



IRRITABILITY AND CONDUCTIVITY 177 

ductorium in action (binding posts 2 and 3), 
and stimulate the nerve with weak induction 
currents. 

The leg will be flexed. 

Use stronger induction shocks. 

As the intensity increases extension as well as 
flexion is seen. A still further increase causes 
extension only. 

The gradations of intensity necessary to show 
these results are sometimes difficult to secure. 
The phenomenon of relative excitability is not lim- 
ited to the case just cited. Weak stimulation of 
the vagus causes adduction of the vocal bands ; 
stronger stimulation, abduction. Weak stimula- 
tion causes opening of the claw of the lobster, while 
stronger stimulation of the same nerve causes clo- 
sure. Weak stimulation of the hypoglossal nerve 
in the dog and rabbit causes the tongue to be thrust 
from the mouth, while with strong stimulation the 
tongue is withdrawn into the mouth. It must not 
be forgotten that the anatomical nerves stimulated 
in these experiments are composed of many axis 
cylinders, each of which is a physiological nerve. 
That they should vary in excitability is to be 
expected. 

A second and probably better explanation of 
the Eitter-Kollett phenomena is found in the dif- 
ference in structure of the flexors and extensors. 

12 



178 GENERAL PROPERTIES OF LIVING TISSUES 

Muscle fibres consist of contractile substance im- 
bedded in sarcoplasm. The relation between 
the contractile substance differs in the same 
muscle in different species and individuals, and 
differs further in the muscles of the same indi- 
vidual. In striated muscles of vertebrates, those 
rich in sarcoplasm have a turbid, opaque appear- 
ance, while those poor in sarcoplasm are translu- 
cent. Important differences in contractility, 
irritability, etc., depend on this difference of 
structure. Muscles which contain many " clear" 
fibres (poor in sarcoplasm) are more irritable 
than those containing many of the fibres rich in 
sarcoplasm. In the flexors of the frog the " clear " 
fibres are relatively more numerous than in the 
extensors. 

Specific Irritability of Nerve Greater than that 
of Muscle. — Arrange an inductorium for single 
induction currents. Make as rapidly as possible 
two nerve-muscle preparations, A and B. Bring 
a wire from the secondary coil to each end of 
muscle A. Let the nerve of B rest on muscle A. 
No stimulation can now reach B except through 
that part of the nerve of B which rests on muscle 
A. Place the secondary some distance from the 
primary coil. Stimulate muscle A with make 
induction shocks, the strength of which is gradu- 
ally increased by approximating the coils. 



IRRITABILITY AND CONDUCTIVITY 179 

Muscle B, which is stimulated only through 
its nerve, will contract before muscle A, which 
is stimulated directly. Hence, the specific irri- 
tability of nerve is greater than that of muscle, 
provided (1) that the intensity of the stimulating 
current is equal for both nerve and muscle, and 
(2) that the irritability of the two muscles does not 
differ, and (3) that the stimulation of the nerve 
of B is not by unipolar induction. The first 
source of error may be excluded, because the 
density of the current passing through the por- 
tion of nerve lying on muscle A is certainly not 
greater than the density of the current passing 
through the muscle itself. The second possibil- 
ity is tested as follows : — 

Eeverse the muscles and repeat the experi- 
ment. 

The result will not be altered. 

The third source of error is excluded as follows. 

Tie a ligature about the nerve of B, between 
muscles A and B. The physiological conduc- 
tivity of nerve B is thereby destroyed, and the 
nerve impulse cannot pass ; but the physical con- 
tinuity of the nerve, and hence its power to con- 
duct electricity, is still present. 

The strongest induction currents applied to 
muscle A will now fail to produce contraction 
of B. 



180 GENERAL PROPERTIES OF LIVING TISSUES 

Irritability at Different Points of Same Nerve. — 

Determine the threshold value for the sciatic 
nerve near the gastrocnemius muscle and about 
two centimetres from the cut end of the nerve. 

The farther from the muscle the nerve is stim- 
ulated, the lower will be the threshold value. It 
has been suggested in explanation of this that 
the nerve impulse gathers force as it passes 
along the nerve, and is the more powerful the 
longer the nerve which it traverses (avalanche 
theory). It has also been suggested that the 
nearer to the nutrient cell of origin the stim- 
ulus is applied, the greater the effect. The true 
explanation lies in the fact that the irritability 
of the nerve is raised in the neighborhood of the 
cross-section by the passage of the demarcation 
current through that portion, as explained on 
page 296. Tigerstedt has shown with mechani- 
cal stimuli that the uninjured nerve has equal 
irritability throughout. 

The Excitation Wave remains in the Muscle or 
Nerve Fibre in which it starts. — In order to 
limit the stimulus to one or two fibres, the 
method of unipolar stimulation may be adopted. 

Fasten in one post of the secondary coil of 
the inductorium arranged for tetanizing currents 
a wire soldered to a blunt needle. The needle, 
except near the free end, and the lower part of 



IRRITABILITY AND CONDUCTIVITY 181 

the connecting wire, should be inclosed in a 
glass tube for insulation. 

Expose the sacral plexus in a brainless frog in 
which the skin has been removed from the hind 
limbs. Connect the preparation by means of a 
copper wire with the earth through the gas or 
water pipes. 

Touch the sacral nerves here and there with 
the needle electrode, watching meanwhile the 
sartorius muscle. 

Partial contractions will be seen in the sar- 
torius, now of the inner, now the outer fibres, 
according to the nerve fibres touched 
by the needle. 

Stimulate the sartorius directly. 
Only the fibres touched by the 
needle contract. 

Evidently the excitation wave re- 
mains limited both in the muscle 
and the nerve to the fibres in which 

Fig. 43. The ., , , 
sartorius. llj auciiLa. 

The same Nerve Fibre may conduct Impulses 
both Centripetally and Centrifugally. — 1. The 
nerve of the sartorius divides at the muscle, part 
going to each half of the muscle (Fig. 43). 
Microscopical examination shows that the divi- 
sion is not simply a parting of individual nerve 
fibres, but that each axis cylinder forks, one 




182 GENERAL PROPERTIES OF LIVING TISSUES 

lirab going upwards, the other downwards. If 
the muscle be severed between the forks, no 
impulse started in one half of the muscle could 
reach the other half, except by going up one 
branch to the original axis cylinder and down 
the remaining branch ; for it is known that the 
nerve impulse does not escape transversely from 
one axis cylinder to other neighboring ones. 

Eemove a sartorius muscle with great care. 
Split the muscle in the middle line for one third 
of its length, beginning at the broad end, as in- 
dicated in the diagram. Stimulate the muscle 
fibres of the right segment mechanically, by 
snipping the preparation with scissors in the 
line a. Do not cut quite through the segment. 

Only the right half twitches. 

Eepeat the stimulus by snipping in the line a v 

Again only the right half twitches. 

Stimulate in the line b. 

Both segments twitch, or at least some fibres 
in each. 

Kepeat at b r 

Both segments twitch again. 

2. The gracilis of the frog is divided into an 
upper, shorter part and a lower, longer part by 
a tendon (Fig. 44, j). Each axis cylinder in 
the nerve N, on approaching the muscle, divides 
into two branches, one of which goes to the 



IRRITABILITY AND CONDUCTIVITY 



183 




Fig. 44. The gracilis. 



upper and the other to the lower portion of the 
muscle. 

Eemove the muscle together with a portion of 
its attached nerve, and examine 
the inner surface (Fig. 44). 
The nerve (N) divides into two 
branches, of which the upper 
(K) runs to the shorter portion 
of the muscle and is unbranched 
for some distance, while the 
other (L) has a very short stem 
and sinks almost at once into the 
substance of the lower part. One of the branches 
(H) perforates the muscle and goes to the skin. 

With a sharp 
pair of scissors cut 
out entirely the part 
shaded in the dia- 
gram, without in- 
juring the nerves. 
The halves of the 
muscle are now 
united only by the 
forked nerve. 

Stimulate the end branches of the 
one of the pieces of muscle by snipping with 
scissors ; also chemically, with a lump of salt. 

Both pieces will contract. 




Fig. 45. 



nerve in 



184 GENERAL PROPERTIES OF LIVING TISSUES 

Speed of Nerve Impulse- — Smoke a drum, and 
adjust it for " spinning." Place two pairs of 
needle electrodes in corks in the moist chamber. 
Arrange the inductorium for maximal make 
currents, placing a simple key and the electro- 
magnetic signal in the primary circuit (Fig. 45). 
Connect the secondary coil to the side cups of 
the pole-changer. Connect the end pairs of 
cups each with one pair of the electrodes in 
the moist chamber. Make a nerve-muscle prep- 
aration, preserving the full length of the sciatic 
nerve. Fasten the femur in the clamp in the 
moist chamber. Connect the Achilles tendon 
to the muscle lever. Bring the point of the 
lever against the drum immediately over the 
writing point of the electro-magnetic signal. 
Let the nerve rest on the electrodes, one 
pair near the end of the nerve, the other 
near the muscle. Spin the drum slowly. 
Hold the writing point of a vibrating tuning 
fork against the smoked paper beneath the 
line drawn by the signal. Send a maximal 
induction current through first one pair of elec- 
trodes and then the other. Determine the inter- 
val between the moment of stimulation and 
the beginning of contraction in each instance. 
[This is done by turning the drum back until 
the writing point of the signal lies precisely in 



IRRITABILITY AND CONDUCTIVITY 185 

the vertical line marked by it when the current 
was made, and then stimulating the muscle to 
contract. The ordinate drawn by the muscle 
lever (the drum being still at rest) will be 
synchronous with the ordinate drawn by the 
signal during the experiment.] 

It will be found that the interval between 
stimulation and contraction is greater when the 
nerve is stimulated far from the muscle than it 
is on stimulation near the muscle. The differ- 
ence is the time occupied by the passage of the 
excitation wave along the nerve between the 
electrodes. 

Measure the length of nerve between the elec- 
trodes, and calculate the speed of the nerve im- 
pulse per second. 

It is assumed in this method that the interval 
between the closure of the primary circuit and 
the beginning of the nerve impulse is the same 
in both instances, and that the interval between 
the arrival of the impulse in the muscle, and the 
visible change of form, is likewise the same in 
both. If the mean and the probable deviation of 
a series of measurements are taken, a fairly accu- 
rate result may be expected. A better method, 
however, is to record the passage of the negative 
variation over a measured length of nerve by 
photographing the meniscus of the capillary 



186 GENERAL PROPERTIES OF LIVING TISSUES 

electrometer. Similar measurements can be 
made with a differential rheotome (page 313). 

Helmholtz found in motor nerves of the- frog 
an average speed of 27 metres per second, but 
the individual variation is considerable. The 
speed is very slow compared with that of light, or 
even sound. It is modified by changes in tem- 
perature, nutrition, anaesthetics (alcohol, ether, 
chloroform, carbon dioxide), the intensity of the 
stimulus, — above a certain value, the greater 
the stimulus, the more rapid the conduction, — 
and by many other factors. Specific differences 
are found depending on the structure of the 
nerve. Thus the velocity has been found in mam- 
malian nerve to smooth muscle to be about 9 
metres per second, while in the bivalve Anodonta 
it is said to be only 1 centimetre per second. 

Apparatus 

Normal saline. Bowl. Towel. Pipette. Glass plate. 
Dry cell. Inductorium. Key. Wires. Frog with sci- 
atic nerve degenerated. Hen's egg incubated 60-70 hours. 
NaCl solution (0.75%). Ligatures. Filter paper. One 
per cent solution of curare. Pole-changer. G-as chamber. 
Carbon dioxide generator. Twenty per cent hydrochloric 
acid. Broken marble. Alcohol. Muscle clamp. Stand. 
Muscle lever with scale pan. Millimetre rule. Ten gram 
weights. Needle electrodes (glass tube). Moist chamber. 
Two pairs of non-polarizable electrodes. Electro-magnetic 
signal. Recording drum. Grlazed paper. Tuning fork. 
Normal saline clav- 



PART II 

THE INCOME OF ENERGY 



PART II 

THE INCOME OF ENERGY 

I FERMENTATION 

Hydrolysis of Starch by Diastase 

Conversion of Starch to Sugar by Germinating 
Barley. — To 5 grams crushed, germinating barley 
add 10 grams potato starch, and 20 c.c. of cold 
water. Then add gradually 70 c.c. of hot water 
with constant stirring. Keep the mixture in a 
temperature of about 60° C. for one hour. 

The insoluble starch will be converted to a 
sweet liquid. 1 

Boil 10 c.c. of Fehling's solution, 2 dilute the 
syrup with water and add it drop by drop to the 
boiling Fehling's solution. 

1 Kirchoff : Schweigger's Journal fur Chemie und Physik, 
1815, xiv, p. 389. There is a small amount of sugar and starch 
in the barley itself. 

2 Fehling's solution. — In a large watch glass weigh 34.639 
gms. pure cupric sulphate (clean crystals). Dissolve the crystals 
by warming them with about 150 c.c. water in an evaporating 
dish. Place the solution in a 500-c.c. measuring flask. Wash the 
remnant from the dish into the flask. Allow the liquid to cool 
completely. Add water to the mark on the neck of the flask. 

Warm about 173 gms. potassium sodium tartrate in a little 
water until dissolved. Place the solution in a 500-c.c. measur- 
ing flask, add 100 c.c. sodium hydroxide, sp. gr. 1.34 (about 
31 per cent), and, after the mixture has completely cooled, fill 
the flask to the mark on the neck. 

In use, mix equal volumes of each solution in a dry glass. 

One molecule grape sugar reduces five molecules cupric oxide 
to cuprous oxide ; 10 c.c. of Fehling's copper sulphate solution 
equals 0.05 gm. grape sugar. 



190 THE INCOME OF ENERGY 

Eed cuprous oxide or its yellow hydrate will 
separate. 

The germinating barley causes the starch to 
take up water, thus changing to a reducing sugar. 
In this instance the agent is a living cell, or 
some substance or " ferment " secreted by the 
cell. It is now necessary to inquire whether 
ferments are separable from living cells. 

Conversion of Starch to Sugar by Salivary Dias- 
tase (Ptyalin). — To 10 c.c. of starch paste 1 col- 
ored blue with iodine (blue iodide of starch) add 
about 2 c.c. of filtered saliva and keep the mixture 
at 35-40° C. 

The starch paste will liquefy and become sweet. 
The blue color will become lighter and finally 
disappear. 

Test with Fehling's solution. Eeduction will 
take place. 

Saliva hydrolyzes starch to a reducing sugar. 

Saliva is secreted by the cells in the salivary 
gland, placed some distance from the mouth. 
The saliva itself contains no secreting cells. 
There are ferments, then, which act at a distance 

1 Starch paste. — Rub 1 gm. potato starch in a mortar with 
25 c.c. cold water. Pour the mixture into an evaporating dish. 
Wash the remnant from the mortar and pestle into the dish with 
75 c.c. water. Heat the mixture to boiling point with constant 
stirring. The starch paste will turn blue upon addition of iodine 
(iodide of starch). 



FERMENTATION 191 

from the cells that produce them. There seems 
thus an important distinction to be made between 
organized ferments, those acting apparently with- 
in the living cell, and unorganized ferments, like 
the salivary diastase, which is secreted by a 
living cell but remains active after leaving the 
cell. It will be seen that this distinction cannot 
be maintained. 

Extraction of Diastase from Germinating Barley. 1 
— Crush freshly germinating barley in a mortar 
with about half its weight of water. Keep the 
mass two hours at 35-40° C. Squeeze out the 
watery extract in a press, or strain by strong 
pressure through a linen cloth. Add excess of 
alcohol. 

Diastase will be precipitated. It may be puri- 
fied by dissolving it in water and reprecipitating 
with alcohol. 

Add a little diastase to 10 c.c. starch paste, 
colored blue with iodine. The starch will be con- 
verted to sugar. The blue color will disappear. 

It appears, therefore, that ferment action is 
not dependent on the life of the cell that secretes 
the ferment. 

Specific Action of Ferments. — The question 
now arises whether the diastase acts only to 

1 Payen and Persoz : Aiinales de chimie et de physique, 
1833, liii, p. 78. 



192 THE INCOME OF ENERGY 

change starch to sugar or whether it causes the 
decomposition of other substances. 

Place a small piece of fibrin in a test-tube and 
add 2 c.c. filtered saliva. . Keep the tube several 
hours at a temperature of 35-40° C. 

The fibrin will not change. 

Place 0.5 c.c. neutral olive oil (page 207) and 2 
c.c. filtered saliva in a test-tube. 

Noteworthy changes will be absent. 

From these experiments it is evident that 
diastase decomposes starches, but does not de- 
compose proteids and fats. Its ferment action is 
thus far " specific." The belief that each ferment 
has its own characteristic product will be in- 
creased by the study of the following typical 
ferment actions. 

Proteid Digestion by Pepsin 

Gastric Digestion of Cooked Beef and Bread. — 

At 7 a.m. feed cooked beef and bread to a cat 
which has fasted twelve hours. At 11 A. M. kill 
the cat, expose the stomach, and apply double 
ligatures about 1 cm. apart to the duodenum at 
the pylorus and to the oesophagus at the cardiac 
orifice. Kemove the stomach. Open the stomach 
very cautiously by drawing a knife along the 
greater curvature. 

" The stomach is very full, and still contains 



FERMENTATION 193 

much meat and bread not wholly softened. The 
softening is greater in the portal region and in 
those portions of the food next the mucous mem- 
brane than in the middle of the stomach contents. 
The mucus secreted by the gastric mucous 
membrane is very abundant and is strongly acid. 
The stomach contents have a sour odor." * 

Artificial Gastric Juice. 2 — 1. Strip the mucous 
membrane from the fourth stomach of a calf. 
Wash the membrane with cold water until the 
acid reaction disappears. Dry the mucous mem- 
brane in the air. Divide some of the dried 
membrane into small pieces and add dilute hy- 
drochloric acid. 3 

2. Strip the mucous membrane of the pig or 
rabbit from the deeper layers of the stomach, cut 
the mucous membrane into the smallest pieces, 
wash slightly with water, pour off the water with 
all possible care, and cover the slightly moist 
residue with glycerine. 4 Before using, add dilute 
hydrochloric acid. 



1 Eberle : Physiologie der Verdauung, 1834, p. 100. 

2 Eberle : loc. cit., p. 79. 

3 Dilute hydrochloric acid. — Add to 10 c.c. officinal HC1, 
sp. gr. 1.124 (about 25 per cent HC1), enough water to make 
1000 c.c. This solution will contain about 0.281 per cent HC1. 
(Salkowski's Practicum, 1893, p. 130.) 

4 Von Wittich: Archiv fur die gesammte Physiologie, 1869, 
ii, p. 194. 

13 



194 THE INCOME OE ENERGY 

Digestion with Artificial Gastric Juice. — Pie- 
pare three flasks, A, B, and C. In A place 100 c.c. 
artificial gastric juice ; in B, 100 c.c. 0.2 per cent 
HC1; and in C, a piece of dried gastric membrane 
and 100 c.c. distilled water. In each of the three 
flasks place a small piece of cooked meat, and keep 
the flasks about five hours at 35-40° C. 1 Com- 
pare the result with that observed in natural 
digestion. 

The artificial gastric juice will digest the meat 
as did the natural juice in the stomach, but neither 
the acid alone, nor the mucous membrane free 
from acid, will digest. There is a ferment in the 
mucous membrane, but it will not act except in 
an acid medium. 

Extraction of Pepsin. — Pepsin more or less con- 
taminated with proteid (pepsin may itself be a proteid) 
may be precipitated from a glycerine extract by alco- 
hol. 2 The pepsin may also be carried down mechani- 
cally by an indifferent precipitate as in Brticke's 
method, 3 in which the mucous membrane, acidulated 
with phosphoric acid, is allowed to digest until the 
proteids are mostly converted into soluble peptone. 
The mixture is then neutralized with lime water. 
The insoluble calcium phosphate thus formed falls as 

1 Eberle : loc. cit. 

2 Von Wittich: loc. cit., p. 195. 

3 Briicke : Sitzungsberichte der konigliche Akademie der 
Wissenschaften zu Wien, 1862, xliii, p. 601. 



FERMENTATION 195 

a fine powder carrying the pepsin with it. The precip- 
itate is dissolved in very dilute hydrochloric acid, and 
to this solution is added a solution of cholesterin in 
alcohol and ether. When the two solutions are mixed, 
the cholesterin separates as an abundant, fine powder 
bearing the pepsin with it. The cholesterin is removed 
with ether, leaving the pepsin. 

Ammonium sulphate may also be used as the me- 
chanical precipitant. 1 

Change of Proteid to Peptone by Pepsin. — 1. 

Place in a test-tube five drops of the glycerine 
extract of pepsin with 5 c.c. 0.2 per cent hydro- 
chloric acid and a small piece of fibrin. 2 Keep 
the mixture at 35-40° C. 

In a short time the fibrin will be dissolved. 
Appropriate tests will show that it has been con- 
verted to peptone. 2. Eepeat the preceding ex- 
periment, using commercial pepsin (never very 
free from proteid). 

Splitting of Casein by Eennin. 

Rennin Extract. — Allow the mucous membrane 
of the stomach (preferably the fourth stomach of 

1 Kiihne and Chittenden: Zeitschrift fur Biologic, 18S6, 
xxii, p. 428. 

2 Preparation of fibrin. — With a bundle of smooth rods 
whip blood as it flows from an artery until the fibrin gathers on 
the rods. Wash the fibrin in running water until the red cor- 
puscles are removed and the fibrin shows its natural color. 
Preserve the fibrin in glycerine. 



196 THE INCOME OF ENERGY 

the suckling calf) to stand twenty-four hours in 
150-200 c.c. 0.1-0.2 per cent solution of hydrochlo- 
ric acid. Then neutralize the acid with great care. 1 

Separation of Rennin. — The extract just prepared 
contains pepsin as well as rennin. The rennin may 
be separated as follows. The neutralized extract is 
repeatedly shaken with fresh amounts of magnesium 
carbonate. The resulting precipitates carry down 
almost all the pepsin and very little rennin. The 
filtrate still rapidly coagulates milk, but contains only 
traces of pepsin. This nitrate is now precipitated 
with lead acetate, the precipitate is decomposed with 
very dilute sulphuric acid, and the mixture filtered. 
To the filtrate, which contains the rennin, is added a 
solution of stearin soap in water. Thereupon the 
soap is thrown out of solution and falls, carrying the 
rennin with it. The soap is then removed by shaking 
with ether, and the rennin remains. 2 

Precipitation of Casein. — Add 1 C.C. of the 
neutral extract to 25 c.c. fresh milk at 36-38° C. 
(Normal milk is amphoteric. If the reaction 
be acid, the acid should be very carefully 
neutralized.) 

In a few minutes the milk will separate into 

1 Hammarsten : Upsala Lakareforenings Forhandlingar, 1872, 
viii, pp. 63-86. Abstract by author in Maly's Jahresbericht 
iiber die Fortschritte der Thierchemie, 1872, ii, pp. 118-125. 

2 Hammarsten : Lehrbuch der physiologischen Chernie, 1895, 
p. 241. 



FERMENTATION 197 

curd and whey. The curd is casein together 
with the fat globules carried down as it precipi- 
tates. The whey is a dilute saline solution of 
milk-albumin, milk sugar, etc. 

Test the chemical reaction. The mixture is 
still neutral. Milk may also be curdled by acid, 
either added artificially or produced in the milk 
itself by lactic acid fermentation of milk sugar. 
The absence of an acid reaction in the above exper- 
iment excludes precipitation through acid fermen- 
tation of milk sugar. Casein prepared free from 
milk sugar is also precipitated by rennin. Finally, 
rennin, extracted by the method given above, does 
not act upon milk sugar, but rapidly precipitates 
casein. 

Analogy suggests that the specific action of 
the rennin may be the splitting of casein and that 
the precipitation may be a secondary process. 
The following experiments determine this matter. 

Experiments of Arthus and Pages. 1 — Prepare 
two solutions, A and B. 



A. 
Milk 100 c.c. 

Neutral oxalate of 

potassium 1 % 5 c.c. 

Rennin 1 to 250 4 c.c. 



B. 
Milk 100 c.c. 

Neutral oxalate of 

potassium 1 % 5 c.c. 
Water 4 c.c. 



1 Arthus and Pages : Archives de physiologic, 1890, p. 334. 



198 THE INCOME OF ENERGY 

(Kennin, 1 to 250, is a pastille of Hansen dis- 
solved in 250 c.c. H 2 0.) 

Keep both mixtures at 38° C. during forty 
minutes. 1. Boil 25 c.c. from each solution. 
Solution A coagulates, while solution B shows 
no trace of coagulation. Hence the action of 
rennin has rendered the casein in A coagulable 
on boiling. 

2. To 25 c.c. from each solution add 8 c.c. of 
a solution of calcium chloride capable of pre- 
cipitating exactly, in equal volumes, the solution 
of potassium oxalate. By this addition any ex- 
cess of potassium oxalate is removed and the 
calcium chloride remains in slight excess. 

A will coagulate ; B will not. Hence the casein 
in solution A has been so changed by rennin that 
it is precipitated on the addition of a small quan- 
tity of calcium chloride. Solution A may also 
be precipitated by restoring its original content 
of calcium chloride, i.e. by adding 5 c.c. of the 
above calcium chloride solution, which will exactly 
combine with the 5^c.c. of potassium oxalate. 

If small quantities of rennin be added to 
natural milk and equal portions of the milk be 
tested from time to time by boiling, the amount 
coagulated will be greater the longer the rennin 
acts. An amount of calcium chloride too small 
to produce coagulation in the early stages of 



FERMENTATION" 199 

rennin action is sufficient to produce coagulation 
when added in the later stages. 

Evidently, in the clotting of milk by rennin 
two separate phenomena must be distinguished: 
(1) the chemical transformation of casein by 
rennin, (2) the precipitation of the transformed 
casein by the calcium chloride. (This salt favors 
also the splitting of the casein.) Rennin may 
therefore be classed with pepsin and trypsin. 

According to Hammarsten the casein is split 
into phosphorus-free albumose and phosphorus- 
holding paracasein. Heat is set free. It is the 
paracasein which precipitates. It is less soluble 
than casein. 

Precipitation of Fibrin by Fibrin Ferment 

Buchanan's Experiment. — Press blood clot 
through a linen cloth. Add the liquid thus ob- 
tained to a serous fluid, which does not clot spon- 
taneously, such as ascitic fluid, pleural effusion, 
hydrocele fluid. 

After some hours a firm, translucent clot will 
form. 1 

Extraction of Fibrin Ferment. Schmidt's Method, 
— Coagulate one part of serum from the blood 

1 Buchanan: London Medical Gazette, 1835, xviii, p. 51; 
idem, 1845, xxxvi, p. 617. This discovery was first announced 
in 1831. 



200 THE INCOME OF ENERGY 

of ox, dog, or horse, by adding 15-20 parts strong 
alcohol. After at least fourteen days, filter, dry 
the moist residue over sulphuric acid, pulverize 
the dried substance, stir it with water (twice the 
volume of the serum originally taken) and after 
allowing sufficient time for solution, filter. The 
filtrate contains the fibrin ferment. 1 

Gamgee's Method. — Allow freshly prepared fi- 
brin (obtained by washing a blood clot free from 
corpuscles) to stand three days in 8.0 per cent 
solution of sodium chloride. Filter. 2 

The filtrate is rich in fibrin ferment. 

Extraction of Fibrinogen. — Eeceive three 
volumes of blood directly from an artery into 
one volume of saturated solution of magnesium 
sulphate, which will prevent the blood from 
clotting. Separate the corpuscles from the liquid 
plasma by the centrifugal machine. Add to the 
plasma an equal volume of saturated solution of 
sodium chloride. Flakes of fibrinogen will be 
precipitated. Filter as quickly as possible, for 
that purpose dividing the liquid among several 
funnels each with a folded filter paper. Press 
the filter papers containing the residue between 
fresh filter paper, in order to remove the adherent 

1 Schmidt : Archiv fur die gesammte Physiol ogie, 1872, vi, 
p. 457. 

2 Ganigee : Journal of physiology, 1879, ii, p. 151. 



FERMENTATION 201 

liquid. Tear the filter containing the fibrinogen 
into small pieces. Dissolve the fibrinogen which 
sticks to the filter as a tough, elastic mass, in a 
quantity of 8 per cent sodium chloride solu- 
tion equal to about one-third the quantity of the 
magnesium sulphate solution originally taken. 
Filter off the fragments of paper. Purify by 
reprecipitation with an equal volume of saturated 
solution of sodium chloride. Filter. Dry as 
before, and add a small quantity of water to the 
finely divided filter to which the precipitate 
clings. This water will take a small quantity of 
salt from the precipitate, and in this dilute saline 
solution the fibrinogen will dissolve. 1 

Precipitation of Fibrinogen by Fibrin Ferment. — 
Add to the dilute saline solution of fibrinogen a 
solution containing fibrin ferment. 

Fibrin will gradually form. 

Ammoniacal Fermentation of Urea by 
Urease 

1. Place 100 c.c. fresh human urine in each 
of three clean flasks marked A, B, C. To B and 
C add 1 c.c. of urine that has become ammonitcal 
upon standing in the atmospheric air. Add also 

1 Hammarsten : Arcliiv fur die gesammte Physiologic, 1879, 
xix, p. 563. Also idem, 1880, xxii, p. 431. Hammarsten's first 
publication was in Nova acta regia societas scientiarura Upsali- 
eusis, 1878, (3), ix. 



202 THE INCOME OF ENERGY 

to G 2 per cent of a saturated solution of carbolic 
acid in water. Let B and G stand in a warm 
place sixteen days. 

2. Withdraw 5 c.c. from flask A. Note 
whether the urine is clear or turbid, and 
whether it effervesces on the addition of a 
dilute acid. Withdraw 2 c.c. from flask A and 
determine its percentage of urea by the hypo- 
bromite method. 

Centrifugalize a portion of the remaining con- 
tents of flask A. With a microscope examine 
the sediment for crystals of ammonio-magnesium 
phosphate and for micro-organisms, especially the 
micrococcus ureee, which occurs in long curved 
chains of round cells about 1.5 p in diameter. 

3. After sixteen days repeat these observa- 
tions on the urine in flasks B and C. Eecord 
the results obtained from all three flasks in the 
table on page 203. 

The table shows that the hydrolysis of urea 
into ammonium carbonate still takes place in 
urine containing enough carbolic acid to destroy 
the micro-organisms long known to be the cause 
of the ammoniacal fermentation. 1 It is therefore 
probably due to a ferment, which escapes from 
the cells after their death. 

1 Hoppe-Seyler : Medicinisch-chemische Untersuchungen, 
Berlin, 1866, p. 570. 



FERMENTATION 



203 



el 

.2 fl 

6 








o .2 1 -2 

«J 2 « "£ 
|| |jf 








Per cent 

of 

Urea. 








Reaction 
to 

Acids. 








Clear 

or 

Turbid. 








Content 

of 

Carbolic 

Acid. 








■a 


A 

Normal 


B 

Septic 


C 
Aseptic 



204 THE INCOME OF ENERGY 

Prior to 1860 ammoniacal decomposition of 
urine was vaguely classed as a fermentation. In 
that year Muller 1 suggested that it might be due 
to a body like beer-yeast. In 1862 Pasteur 2 
discovered such a yeast, which he called Torula 
urece. Cohn first classed it with the micrococci. 
It is aerobic. Miguel finds seven species of 
bacilli, nine micrococci, and one sarcina, that 
decompose urea. These obtain their nitrogen 
ordinarily from proteids, but in the absence of 
proteids may utilize urea. 

Extraction of Urease. — To 10 C.C. of urine 
undergoing an active ammoniacal fermentation, 
add 50 c.c. of strong alcohol, and allow the 
mixture to stand in a well-corked flask. After 
five days place the precipitate upon a very small 
filter and wash it with 50 c.c. of fresh alcohol. 
(Preserve both filtrates for recovery of the alcohol 
by redistillation.) 

1. Add a very small quantity of this precip- 
itate to a neutral 2 per cent solution of urea. 
Test the reaction. Place the mixture in a water 
bath at 38° C. 

After a few minutes again test the reaction. 

It will be strongly alkaline. 

1 Muller: Journal fur praktische Chemie, 1860, lxxxi, p. 467. 

2 Pasteur : Comptes rendus de l'academie des sciences, Paris, 
1860, 1, p. 869. See also Van Tieghem, idem, 1864, p. 210. 



FERMENTATION 205 

After a short time the odor of ammonia will be 
perceptible. The alcoholic precipitate contains a 
ferment capable of quickly hydrating urea. 

"The alcoholic precipitate from the unfiltered 
urine consists chiefly of various salts together 
with the cells of the Torula, hence when treated 
with water some of the salts are dissolved and 
pass with the ferment through the filter. If this 
first aqueous extract be again precipitated with 
alcohol, a portion of the salts will be again 
removed, and if this second precipitate be several 
times redissolved in water and reprecipitated 
with alcohol, the body with the ferment proper- 
ties may be ultimately separated — as an amor- 
phous white powder soluble to a clear solution 
in distilled water and not characterized by any 
special chemical reactions." 

The ferment is not secreted by the cells into 
the surrounding liquid, but is retained within the 
cell bodies, for the living cells may be filtered off, 
and the filtrate will not hydrate the urea. 1 

Splitting and Synthesis of Fats 

Chemistry of Fats and Soaps. — When olive oil 
is saponified, glycerine appears (Scheele, 1779). 

1 Lea : Journal of Physiology, 1885, vi, p. 138. See also 
Musculus : Comptes rendus de l'acadenrie des sciences, Paris, 
1874, lxxviii, p. 132 ; idem, 1876, lxxxii, p. 333 ; Archiv fur 
die gesamnite Physiologie, 1876, xii, p. 214. 



206 THE INCOME OF ENERGY 

It is related to the alcohols (Chevreul, 1813), 
being a compound ether or ester, a combination 
of an alcohol with an acid. Commercially gly- 
cerine is prepared by exposing neutral fats, such 
as stearin, to superheated steam, whereby the 
neutral fat is split into glycerine and fatty acid. 



CH 2 

1 


•CO(CH 2 ) 16 


CH 3 




H 


'OH 




CHO 

] 


• CO(CH 2 ) 16 


■CH 3 


+ 


H 


■OH 


= 


CH 2 


•CO(CH 2 ) 16 


■CH 3 




H 


•OH 






STEARIN 






WATER 








CH 2 


•OH 




CO 


■OH(CH 2 ) 16 -CH 






CH 


•OH 


+ 


CO 

i 


■ OH(CH 2 ) 16 ' CH f 






CH 2 


•OH 




60 


• OH(CH 2 ) 16 • CH< 






GLYCERINE 






STEARIC ACID 



If an alkali be present, it will combine with 
the fatty acid to form a soap. 



CO 


•OH(CH 2 ) 16 -CH 3 


Na-OH 




CO 


OH(CH 2 ) 16 -CH 3 


+ Na • OH = 




CO 


•OH(CH 2 ) 16 -CH 3 


Na-OH 






STEARIC ACID 


SODIUM 
HYDROXIDE 








CO-ONa(CH 2 ) 16 -CH 3 


HOH 






CO'ONa(CH 2 ) 16 -CH 3 + 


H-OH 






CO-ONa(CH 2 ) 16 .CH 3 


H-OH 






SODIUM STEARATE 


WATER 



Splitting of Fats by the Pancreatic Juice. Ber- 
nard's Experiment — Place 2 c.c. neutral olive 



FERMENTATION 207 

oil in a test-tube and add a small quantity of 
pancreatic juice (or a piece of fresh pancreas or 
extract of pancreas). Test the reaction of the 
mixture. It is alkaline. Note that a white, 
creamy liquid forms almost immediately. This 
" emulsion " is composed of a multitude of small 
fat globules. 

Test the reaction again. It gradually becomes 
acid. 

It is evident that under the influence of the 
pancreatic juice the fatty matter is not simply 
finely divided and emulsified, but that it has also 
been modified chemically. 1 

In order to study the splitting of neutral fats 
by lipase, a ferment found in the pancreatic juice, 
it is necessary (1) to prepare a perfectly neutral 
fat, and (2) to recognize the fatty acid as soon as 
it is set free. 

Preparation of Neutral Fat. — Shake commer- 
cial olive oil (which always contains fatty acid) 
for two hours at 95° C. in a separating funnel 
with a saturated solution of barium hydroxide. 
Allow the mixture to stand until the oil sepa- 
rates from the hydroxide. Kemove the hydrox- 
ide. Filter the oil. 

The Emulsion Test for Fatty Acid. Briicke's 

1 Bernard : Comptes rendus de l'academie des sciences, Paris, 
1849, xxviii, p. 250. 



208 THE INCOME OF ENERGY 

Experiment. — 1. Shake 1 c.c. neutral olive oil 
in a test-tube with 5 c.c. 0.25 per cent sodium 
carbonate solution. 

The oil will be broken up into large globules 
which will speedily reunite, leaving the liquid 
clear. 

2. Shake 1 c.c. rancid olive oil (containing 
about 5.5 per cent fatty acid) with 5 c.c. 0.25 per 
cent sodium carbonate solution. 

The mixture becomes instantly milky. The 
oil is divided into globules of microscopic size. 
The emulsion is permanent. 

3. Shake 1 c.c. neutral olive oil with 5 c.c. water. 
The water and oil will not mix. 

4. Shake 1 c.c. neutral oil with water con- 
taining soap. 

The oil will be emulsified. It is probable 
therefore that soap contributes to the emulsion, 
perhaps by coating the fine, particles of oil with a 
membrane that prevents their reunion. 1 

Gad's Experiment. — 1 . Fill a watch glass 
about 5 cm. in diameter with 0.25 per cent solu- 
tion of sodium carbonate. With a glass rod 
carefully place a large drop of rancid olive oil 
(containing 5.5 per cent fatty acid) upon the 
surface of the soda solution. 

1 Briieke : Sitzungsberichte der kaiserliclien Akademie der 
Wissenschaften zu Wien, 1870, lxi, pp. 613-614. 



FERMENTATION 209 

The drop will come to rest, and for a moment 
both the drop and the surrounding liquid remain 
clear. Very soon, however, the oil is covered 
with a white layer, and through the soda solu- 
tion spreads a white cloud which becomes denser 
and denser until the oil drop, steadily diminish- 
ing in size, floats in a milky white liquid. 

2. Eepeat the experiment, observing the oil 
drop under a low power of the microscope. 

Note the extraordinary motion in the neigh- 
borhood of the oil drop, and how the particles of 
oil are thrown out in strong eddies. 

3. Examine the completed emulsion under a 
higher power of the microscope. 

There appear exceedingly small fat drops of 
very uniform size. The milky fluid is the finest 
and most uniform emulsion. 1 

Hachford's Experiment. — " Arrange a series of 
watch glasses containing 0.25 per cent solution 
sodium carbonate. Place in a test-tube 2 c.c. 
neutral olive oil and 1 c.c. pancreatic juice (or 
extract). Shake the tube and allow the juice 
and oil to separate, then pipette a drop of oil 
from the surface and place it on the soda solu- 
tion in watch glass 1. Again shake the tube 
and allow the oil and juice to separate, then 
pipette as before, placing a drop of oil in watch 

1 Gad: Archiv fur Physiologic, 1878, p. 183. 
14 



210 THE INCOME OF ENERGY 

glass 2. Again shake and pipette as before, and 
repeat this process every three or four minutes 
until the experiment is completed. The begin- 
ning of the experiment and the time of each 
pipetting must be carefully noted. If the pipet- 
tings are three minutes apart, then the first drop 
of oil will have been exposed three minutes to 
the action of the pancreatic juice, the second 
drop six minutes, the third nine minutes, and 
so on. 1 

The gradual increase in fatty acid will be 
shown by the gradual increase in the amount 
of the spontaneous emulsion. 2 

It has just been shown that lipase will hydro- 
lyze neutral fats into fatty acid and glycerine. 
We must now enquire whether this ferment 
can effect the synthesis of fats, in other words 
whether its action is reversible. Tor this pur- 

1 Each ford : Journal of physiology, 1891, xii, p. 81. Each- 
ford used J c.c. fresh pancreatic juice obtained by placing a 
glass tube in the pancreatic duct of the rabbit (see page 80). 

2 " There is a possible error in this method which had better 
be spoken of here. It would seem that the alkali of the pan- 
creatic juice would combine with the fatty acids forming soap, 
and in this way the oil would soon be emulsified in the juice 
itself and not separate after shaking. This would indeed be a 
serious drawback if it actually occurred, but in truth it does not 
occur until late in the experiment after we have obtained the 
information we have sought by the spontaneous emulsion 
method." (Rachford, loc. cit., p. 82). 



FERMENTATION 211 

pose an extract of lipase may be used, first, to 
split a neutral fat (or glycerol ester) into its con- 
stituent fatty acid and alcohol (glycerine is a 
trihydric alcohol), and second, to form a neutral 
fat from fatty acid and alcohol. 

Extraction of Lipase. From Pancreas. — Ee- 
move the pancreas of the pig within thirty min- 
utes after the death of the animal. Dissect off 
as much of the fat as possible. Eeduce the pan- 
creas to a fine pulp in a mortar with coarse well- 
washed white sand. Extract the lipase with a 
little water or glycerine. 

From Liver. — Eemove the liver of the pig 
within thirty minutes of the death of the animal. 
Eeduce 50 gms. to a fine pulp in a mortar with 
about 200 c.c. water. Filter. Dilute the watery 
extract to 500 c.c. 

Hydrolysis of Ethyl Butyrate by Lipase. — 
Place in each of two test-tubes, A and B, 4 c.c. 
water, 0.1 c.c. toluene, 1 and 0.26 c.c. ethyl buty- 
rate. 2 Cork the tubes tightly. Place them in the 
water bath for five minutes, to bring them to 
the temperature of the bath, 40° C. Add 1 c.c. of 

1 Toluene is an antiseptic, which prevents the splitting of 
the neutral fat by bacteria. 

2 Ethyl butyrate hydrolyzes more rapidly than butter fat. 
It has the further advantage that the amount split by the 
temperatures employed during the time of the experiment is too 
small to be measurable. 



212 THE INCOME OF ENERGY 

the aqueous extract of lipase to each. Boil tube 
B. Place both tubes at 40° C. for fifteen min- 
utes. Remove them from the bath and plunge 
them into ice-water (to check further ferment 
action). Titrate with ^ KOH, using neutral lit- 
mus as the indicator. 1 The initial acidity of the 

1 A normal solution contains in each litre one equivalent 
weight of the active substance, i. e. that mass of the active sub- 
stance which is equivalent to the atomic weight of a univalent 
element in the reaction for which the normal solution is to be 
employed. Equal volumes of different normal solutions are 
equivalent to each other. Thus, 1 c.c. normal alkali solution 
requires for neutralization exactly 1 c.c. normal acid, no matter 
what acid is employed to make the normal solution. 

Preparation of Normal Potassium Solution. — The content of 
KOH in 1 litre is 56.16 grams. Dissolve 60 gms. purest com- 
mercial KOH (which always contains considerable water) in a 
graduated cylinder in about 950 c.c. water. Determine the 
true content of KOH by titration with a normal oxalic acid 
solution (prepared by dissolving its equivalent weight 63 gms. 
in 1 litre water) as follows. Thoroughly stir the potassium hy- 
droxide solution, fill a burette with a portion of the well-mixed 
solution. Place 10 c.c. normal oxalic acid solution in a beaker 
and add a few drops of solution of rosolic acid as indicator. 
Add the alkali from the burette cautiously until the end point 
of the reaction is reached, i. e. until the indicator gives a red 
color which does not quickly disappear. As 10 c.c. of acid solu- 
tion should exactly neutralize 10 c.c. of alkali solution, pro- 
vided both were normal, it follows that the quantity of KOH 
solution necessary to neutralize is to 10 c.c. as the total quantity 
of the original KOH solution is to x. x will be the number of 
cubic centimetres to which the KOH solution must be diluted 
in order to make it normal. A portion of the normal solution 
should then be diluted 1:20, and preserved in an air-tight 



FERMENTATION 213 

enzyme solution, usually 0.1 to 0.2 c.c. ■£-$ KOH, 
should be deducted from the cubic centimetres 
KOH required to neutralize the fatty acid 
formed. 1 

Fatty acid will appear in tube A, but not in 
tube B, in which the enzyme was destroyed by 
boiling. 

Synthesis of Neutral Fat by Lipase. — 1. Place 
5 c.c. T ^ butyric acid, 2 c.c. 13 per cent alcohol, 
1 c.c. diluted glycerine extract of pig's pancreas 
(or aqueous extract of liver) in each of two test- 
tubes, A and B. Boil the contents of test-tube 
B. Seal both tubes. Keep them thirty-six 
hours at 48.5° C. 

On opening the tubes, A will give a distinct 
odor of ethyl butyrate ; none will be found in B, 
in which the ferment was destroyed by boiling. 2 

2. Place 5 gms. glycerine, 2 gms. isobutyric 
acid, 125 gms. water, 1 c.c. neutralized blood serum 
(or aqueous extract of pig's liver) in each of two 

flask. (Compare Miiller and Kiliani: Kurzes Lehrbuch der 
analytischen Chemie, 1900, p. 31 and p. 83). 

At 30° (summer temperature) 0.26 c.c. ethyl butyrate weighs 
0.2300 gram. This quantity, if completely hydrolyzed, would 
require 39.7 c.c. jfo KOH. 

1 Kastle and Loevenhart : American chemical journal, 1900, 
xxiv, pp. 491-525. Also Loevenhart : American journal of 
physiology, 1902, vi, pp. 331-350. 

2 Kastle and Loevenhart : loc. cit., p. 518. 



214 THE INCOME OF ENERGY 

test-tubes, A and B. Boil the contents of tube 
B. Place both at 37° C. At intervals of half 
an hour titrate a portion from each tube with 
2% KOH solution. The acidity will diminish in 
both, but much more rapidly in the tube contain- 
ing the active ferment. 

The acidity is diminished by the combination 
of the fatty acid with the glycerine to form a 
neutral fat. 1 

Fats are hydrolyzed to some extent in the stomach, 2 
but stomach lipase is active only in neutral solutions. 
It is inhibited or destroyed by 0.3 per cent hydro- 
chloric acid. Other ethereal salts besides the fats are 
hydrolyzed in the intestine, e. g. salol. 8 

The rate of change by lipase increases with the 
amount of the enzyme present. 4 

Reversible action is seen in ferments other than 
lipase, as in the following experiments. 

Splitting of Hippuric Acid by Histozyme. — A pig's 
kidney was perfused four hours with one litre defibri- 
nated pig's blood to which 0.8 gram hippuric acid 

1 Hanriot : Comptes rendus de la societe de biologie, 1901, 
p. 70. 

2 Marcet: Proceedings Royal Society, London, 1858, ix, 
p. 306. Ogata : Archiv fiir Physiologie, 1881, p. 515. Cash : 
Archiv fiir Physiologie, 1880, p. 323. 

3 Baas: Zeitschrift fur physiologische Chemie, 1890, xiv, 
p. 416. 

4 Kastle and Loevenhart : loc. cit., p. 511. 



FERMENTATION 215 

(sodium salt) had been added. The blood passed 
through the kidney 9-10 times. 

Upon analysis, there appeared 0.0S7 gram benzoic 
acid, produced from 0.1276 gram hippuric acid. 

Synthesis of Hippuric Acid by Histozyme. — A pig's 
kidney was perfused three hours with one litre defibri- 
nated pig's blood containing a neutral solution of 0.5 
gram benzoic acid and 0.6 gram glycocoll. The blood 
passed ten times through the kidney. 

Found : 94 mgm. hippuric acid. 1 

These actions depend upon a ferment, histozyme, 
extracted by Schmiedeberg. 

Some hypothetical considerations will be of value 
here. Compounds of carbon may be divided into 
those in which the carbon atoms are arranged in an 
open chain, for example ethane, C 2 H 6 , 

H H 

H— C— C— H 

I I 
H H 



and those in which the chain is closed to form a "car- 
bon ring," for example, benzene, C 6 H 6 , which consists 
of six carbon atoms, in a closed, ring-shaped chain, the 
"benzene nucleus," with a hydrogen atom joined 
to each carbon atom by its fourth affinity (Kekule, 
1865). 

1 Schmiedeberg : Archiv fiir experimentelle Pathologie und 
Pharniakologie, 1881, xiv, pp. 382-383. 



H 


H 


\ ■ 


/ 


C = 


= C 


/ 


\ 


c 


c 


^ 


// 


c- 


-c 


/ 


\ 


H 


H 



216 THE INCOME OF ENERGY 



\ / 

c = c 
/ \ 
-C C- H -C 

% // 

c-c 
/ \ 

BENZENE NUCLEUS 
OR RING 



The benzene ring is not easily opened, but deriva- 
tives of benzene may be readily obtained by replacing 
hydrogen atoms. Thus, in aniline or amido-benzene, 
C 6 H 5 .NH 2 , one hydrogen atom is replaced by amide 
radical ; in carbolic acid, or phenol, C 6 H 5 .OH, by 
hydroxyl ; in toluene or methyl benzene, C 6 H 5 .CH 3 , 
by the radical CH 3 . The carbon atom in methyl 
benzene is not a part of the benzene ring, but is 
chained to the side of the ring. The hydrogen atoms 
in the side-chain differ in their affinities from those 
attached to the ring; the hydrogen in the ring may 
be replaced by groups (e.#. N0 2 ) which will not readily 
replace the hydrogen of the side-chain. This is a 
matter of special interest in relation to the specific 
action of poisons, ferments, etc. By substituting 
hydroxyl for the hydrogen of the side-chain, benzyl 
alcohol, C 6 H 5 .CH 2 .OH, is formed. By introducing 
carboxyl, benzoic acid, C 6 H 5 .CO.OH, is obtained. It 
has been shown above that benzoic acid and glyco- 
coll are united in the kidney to form hippuric acid. 
Glycocoll is amido-acetic acid, CH 2 (NH 2 ).CO.OH. It 



FERMENTATION 217 

unites with benzoic acid by replacing the hydroxyl in 
the side-chain, thus forming 

C 6 H 5 .CO.NH x 

eo.oH 

HIPPURIC ACID 

Cinnamic acid, toluene, and other aromatic substances 
are similarly excreted as hippuric acid when taken 
internally. 

The reversible action of the kidney ferment is im- 
portant in hastening the establishment of the equi- 
librium between benzoic acid and glycocoll. If these 
two bodies pass through the kidney, a certain amount 
of hippuric acid is formed ; if hippuric acid itself 
passes through the kidney, a certain quantity is hy- 
drolyzed. 

Relation of Reversible Action to Absorption of Fat. — 
"Pancreatic juice is capable of hydrolyzing all the fat 
of a fatty meal in the period of pancreatic digestion. 
In the living intestine the hydrolysis should be com- 
plete, inasmuch as the removal of the products of the 
hydrolysis by absorption prevents the establishment 
of equilibrium. On the other hand, the products of 
the hydrolysis in their transition through the epithelial 
cells come in contact with a lipolytic enzyme, the pres- 
ence of which in these cells has been demonstrated in 
the above. 

"The lipase now finds itself in contact with only 
fatty acid and glycerine, and hence in acting catalyti- 
cally to bring about the chemical equilibrium, it effects 



218 THE INCOME OF ENERGY 

the synthesis of a fat. This would offer a satisfactory 
explanation of the presence of fat granules in these 
cells. As the fatty acid and glycerine diffuse out of 
the cells through the basement membrane, the fat 
in these cells would speedily disappear were it not that 
these substances were constantly being absorbed from 
the lumen of the intestine. AVhen absorption ceases, 
however, the fat present is at once hydrolyzed by the 
lipase present. This hydrolysis is in all probability 
complete for the reason that the products of the 
hydrolysis, viz., glycerine and fatty acid, are being 
constantly removed by diffusion. According to this 
view, therefore, no fat ever enters or leaves the epi- 
thelial cells as such, but as fatty acid and glycerine. 

"These two substances then enter the central 
lacteal, where equilibrium is again established and 
there is a large production of fat." 1 

Immunity 

Ehrlich's Ricin Experiments. 2 — Powder Albert 
biscuits weighing 6.75 grams. Add to each cake 

1 Kastle and Loevenhart: loc cit., p. 522. 

2 Ehrlich : Deutsche medicinische Wochenschrift, 1891, 
xvii, pp. 976-979. 

Ricin is a toxalbumin extracted from the seeds of the castor 
oil plant. It is poisonous in the slightest traces. Weight for 
weight it is a billion times more poisonous than corrosive sub- 
limate. Intravenous injection of 0.03 milligram (0.00003 gram) 
per kilo of body weight is fatal. One gram commercial ricin 
would kill one and one-half million guinea-pigs. The effect is 
about one hundred times less when taken by the mouth, yet 



FERMENTATION 219 

3.2-3.5 c.c. of water containing rksin. The be- 
ginning content of ricin should be 0.02 gm. ricin 
for each cake ; 0.035 gm. is fatal in the course 
of five or six days. Mix the biscuit powder and 
ricin solution to a stiff dough, roll the dough into 
rods, divide them into equal lengths, and dry 
the portions quickly on a wire sieve. Determine 
the effect on white mice of successively increas- 
ing doses, as follows : 



DAY 


DOSE 


1 


0:002 gm. 


2 


. . . 


3 


0.006 


4 


0.008 


5 


... 


6 


0.01 


7 


0.0125 


8 


0.015 



DAY 


DOSE 


9 


0.02 


10 


, 0.03 


11 


0.04 


12 


0.05 


13 


0.06 


14 


... 


15 


0.08 


16 


0.01 


;anec 


>usly a fi 


cof 


a 2ir<roo" 



mouse with the fatal dose — 1 c.c. of a ^Woo^ o" so ~ 
lution per 20 gm. of mouse. At the same time 

even thus 0.18 gram will kill a full-grown man. The cause of 
death is agglutination of red blood corpuscles, and hence 
multiple thrombosis, especially of the abdominal vessels. 
Clinically, violent diarrhoea and progressive exhaustion are ob- 
served. The toxicity is greatly dependent on species. Guinea- 
pigs are far more susceptible than white mice. With white 
mice the fatal subcutaneous injection is 1 c.c. of a solution con- 
taining Tjjn^tf ricin per 20 grams of body weight. 



220 THE INCOME OF ENERGY 

inject the immunized mice with a dose one 
hundred times as great. 1 

Observe the non-immune and the immune mice 
for several days and note the results. 

Ehrlich continued the above experiment until the 
immunized mouse received daily 0.5 gm. of the ricin 
by the mouth. Such animals bore safely subcutaneous 
injections of 5^ and even more. The immunity also 
appeared in that solutions of 0.5-1.0 per cent applied 
to the eyes of non-immune mice caused violent pano- 
phthalmitis, while immune mice bore easily the appli- 
cation of 10 per cent solutions. 

This absolute local immunity was fully established 
when the general immunity had attained only a 
middle grade. Normally the subcutaneous injection 
of 40 oV ou ricin solution causes severe local inflamma- 
tion, but thoroughly immunized animals bear T qV . 
Quantitative experiments show that the resistance to 
the poison is not increased during the first four days, 
and the increase is doubtful on the fifth day, but on 
the sixth day a relatively high (for example thirteen- 
fold) general immunity is suddenly established. The 
sudden fall toward normal temperature observed in 
diseases with a "crisis," such as pneumonia, may de- 
pend on the " critical " establishment of immunity. 

Immunity is not increased by continued administra- 
tion of the same dose, day by day. An equilibrium 
appears to be established. 

1 The mice in these experiments must be carefully protected 
against cold and wetting. 



FERMENTATION 221 

The immunity once established endures a consider- 
able time ; six months and possibly much longer. 

Ricin Antitoxine. — Defibrinate the blood of the 
immunized mice. Divide it into two portions. 
1. To one portion add ricin solution in such a 
ratio that the mixture shall contain yqWo o> *• e - 
twice the fatal amount. 

Inject a fresh mouse subcutaneously with 1 c.c. 
of this mixture per 20 grams of weight. 

The poison will be borne. It has been neu- 
tralized by the serum of the immune animal. 
This result accords with the discovery of Behring 
and Kitasato that immunity in diphtheria and 
tetanus depends on the power of the serum to 
neutralize the poison. 

2. Divide the second portion of the antitoxine 
blood among six small test-tubes. To the first 
add a few drops tU"oVo "o r i cm solution. To the 
others add amounts increasing in a definite ratio. 

At first there will be no effect (immunity). 
As the amount of ricin added is increased, a point 
will be reached at which agglutination of red 
corpusles will be produced. This is the neutrali- 
zation point. 

Evidently, there is a definite quantitative 
chemical relation between the toxine and the 
antitoxine. 



222 THE INCOME OF ENERGY 

Theory of Immunity. 1 — Jenner discovered the 
protective action of vaccinia against small-pox. The 
small-pox virus when passed through a susceptible 
animal becomes attenuated. This weakened poison 
introduced into the circulation in man protects the 
individual for long periods against the original disease 
— it establishes an artificial immunity against small- 
pox. Schwann found that fermentation and putre- 
faction arose through the agency of micro-organisms 
coming from without. Pasteur and Koch demonstrated 
that the inoculation of animals with pure cultures of 
certain bacteria produced specific infectious diseases, 
and that these cultures could be modified at will, 
either by passing through the animal body, as in 
Jenner's method, or in artificial culture media. Pas- 
teur produced artificial immunity by using attenuated 
virus. Behring discovered that the blood-serum of 
animals immunized against diphtheria contained a sub- 
stance which would protect other animals against the 
toxine of diphtheria. So also with tetanus. Ehrlich 
introduced the quantitative study of toxines and anti- 
toxines by means of test-tube experiments, thereby 
eliminating the uncertain factor of the animal body. 
Thus it was shown in experiments on tetanus toxine 
that the action of antitoxines is accelerated by heat, 
retarded by cold, dependent on concentration — in 
short, that it is a chemical action. In the above ex- 
periments on ricin, it is shown that the relation 

1 Ehrlich : Croonian Lecture, Proceedings of the Royal 
Society, London, 1901, lxvi, pp. 424-448. 



FERMENTATION 223 

between toxine and antitoxine is quantitative. These 
results, obtained by test-tube experiments, have been 
confirmed by observations on living animals. Thus it 
was established that a fixed quantity of toxine is neu- 
tralized by a fixed quantity of its specific antitoxine. 

Chemical substances affect only those tissues with 
which they are able to come into chemical contact. 
They must first reach the tissue. This general law is 
illustrated by the experiments of Donitz with tetanus 
toxine. 1 When the toxine is injected directly into 
the circulation and immediately followed by a chemi- 
cally equivalent amount of antitoxine, the animal is 
not poisoned ; all the toxine circulating in the blood 
is neutralized. When the same neutralizing dose is 
injected eight minutes after the toxine, death occurs 
from tetanus exactly as if no antitoxine had been used. 
In these eight minutes a lethal quantity of toxine 
must have left the blood and entered the tissues. 
This toxine which has entered the tissues may still 
for a time be withdrawn by injection of the specific 
antitoxine in quantities much greater than the simple 
neutralizing dose. The longer the delay, the larger 
the saving dose. But after a fixed interval, or " period 
of incubation," no amount of antitoxine, however 
large, will prevent tetanus. There must, therefore, 
be present in the brain or cord (the organ princi- 
pally affected by tetanus toxine) certain atom groups 
which, like the antitoxine, have a chemical affinity 
for the toxine. At the close of the period of incuba- 

1 Donitz : Klinisches Jahrbucb, 1900, vii. 



224 THE INCOME OF ENERGY 

tion the chemical union between these atom groups 
and the toxine is complete and the antitoxine is shut 
out. Wassermann x found that when tetanus toxine 
was mixed with fresh brain or cord substance from the 
guinea-pig, the toxine united chemically with the nerve 
centres so that neither the surrounding liquid nor the 
mixture itself was poisonous when injected into an 
animal. 

The stable benzene ring and the less stable side-chains 
of the benzene derivatives 2 suggested to Ehrlich that 
living cells also consist of a stable centre and less stable 
side-chains. The side-chains enable the cell to form 
chemical combinations with food stuffs and other bodies 
that possess atom groups having a chemical affinity 
with the atom groups in the side-chains. It is in this 
way that the toxine is bound to the cell. Experiments 
have shown that the binding atoms in the toxine 
molecule are not the poison atoms. If for a portion 
of fresh toxine there be determined quantitatively (1) 
the killing power and (2) the amount of antitoxine 
required to neutralize the toxine, aod if the remainder 
of the toxine be then allowed to stand for a time, it 
will be found, on again determining the toxic power 
and the combining power, that the toxic power has di- 
minished, while the combining power remains almost 
the same. Hence, two separate and independent groups 
exist. Ehrlich terms the combining atoms the hapto- 
phore group, while the poison atoms are the toxophore 

1 Wassermann : Berliner klinische Wochenschrift, 1898. 

2 See page 216. 



FERMENTATION 225 

group. The haptophore atom group (own-to, I cling to) 
unites with the antitoxine, if there be any present, or 
with any other atom group for which it has chemical 
affinity. If this latter atom group be in the side-chain 
of a living cell, its union with the haptophore atoms 
of the toxine will necessarily bring the poison atoms of 
the toxine into intimate chemical relationship with the 
central atoms of the cell. Poisoning will then take 
place. If the cells of vital organs have no atom groups 
with chemical affinity for the haptophore group of a 
toxine, no union between cell-atom group and hapto- 
phore takes place, the toxophore is not brought into 
intimate contact with the cell, and poisoning does 
not occur. The animal is naturally immune to this 
particular toxine. Thus a toxine in sausages is exces- 
sively poisonous to man, the monkey, and the rabbit, 
while even large amounts are not injurious to the 
dog. 

The haptophore group of the toxine acts immediately 
after injection into the organism, while in most or all 
toxines the toxophore group becomes active only after 
a longer or shorter incubation period. During this 
period the animal may often be saved by placing it in 
conditions in which the toxophores cannot act. Thus 
frogs kept at less than 20° C. are not poisoned by large 
doses of tetanus toxine, though much smaller doses are 
fatal at a higher temperature (Morgenroth). 

The toxophile atom group of the cell was not pre- 
destined to unite with a remotely possible toxine, — 
it has a normal function, probably that of attaching 
food to the cell. When it enters into its linn and 

15 



226 THE INCOME OF ENERGY 

enduring union with the haptophore group of a toxine, . 
this normal function is lost. Such a loss acts as a 
physiological stimulus. 1 ]\ T ew side-chains are produced 
by the cell, only to unite with fresh toxine. The pro- 
duction and the loss of side-chains continue until all 
the toxine in the blood is neutralized. By this time 
the cell has become habituated to a more than normal 
production of these special atom groups. The excess 
is cast off like a secretion and circulates in the blood. 
These free side-chains, possessing a special affinity for 
one specific toxine, constitute the antitoxine of that 
toxine. 

Their continued production after the neutralization 
of all the toxine protects the animal against fresh 
toxine, i. e. establishes continued immunity. 

It has already been stated that by special means the 
toxophore group of a toxine may be weakened or 
destroyed while its haptophore group is unchanged. 
Such altered and non-poisonous toxines are termed 
toxoids. As their affinity for the side-chains of the 
cells remains unaltered, the toxoids by continuing to 
unite with the side-chains of the cells may stimulate 
the production of such side-chains in excess, or, in 
other words, may assist in making antitoxine and thus 
establishing immunity. 

1 Weigert : Deutsche medicinische Wochenschrift, 1896. 



fermentation 227 

Haemolytig and Bacteriolytic Ferments 

Bordet's Experiments. 1 — Inject into the perito- 
neum of a guinea-pig 10 c.c. defibrinated rabbit 
blood on five successive days. After two more 
days bleed the guinea-pig and obtain the serum, 
by allowing the blood to stand in test-tubes in a 
cool place until the shrinking clot has pressed 
out the serum. 

1. Mix a drop of serum from a fresh guinea- 
pig (one not injected with rabbit blood) with a 
drop of defibrinated rabbit blood and examine 
under the microscope. The corpuscles show a 
very slight agglutination, but are otherwise un- 
injured. The normal serum of the guinea-pig is 
almost inactive upon rabbit blood. 

2. A. Mix a drop of the serum from the 
injected guinea-pig with a drop of defibrinated 
rabbit blood and examine under the microscope. 
The corpuscles are strongly agglutinated. 2 

B. Mix 0.5 c.c. of the serum with 1.5 c.c. 
defibrinated rabbit blood. 

1 Bordet: Amiales de 1'Instittet Pasteur, 1898, xii, pp. 692- 
694. 

2 Agglutinated blood looks granular, especially on gentle 
shaking ; the massed corpuscles sink rapidly ; the}' will not pass 
through filter paper. Agglutination of blood corpuscles is 
similar to the clumping of the typhoid bacillus in the serum of 
a typhoid-fever patient. 



228 THE INCOME OF ENERGY 

The corpuscles are agglutinated and their hae- 
moglobin is set free. The mixture becomes red, 
clear and limpid in two or three minutes. With 
the microscope nothing can be found but the 
stroma of the corpuscles, more or less deformed, 
very transparent and scarcely visible. 

The continued presence of blood corpuscles 
of the rabbit in the blood of the guinea-pig has 
developed in the latter the power to agglutinate 
the corpuscles and to set free their haemoglobin. 
It is thus that the guinea-pig protects itself ; it 
acquires immunity. 

3. Heat 1 c.c. of serum to 55° C. for half an 
hour. Add 0.5 c.c. of this to 1.5 c.c. defibrinated 
rabbit blood as in Experiment 2 B. 

The serum which was heated to 55° C. no 
longer destroys the corpuscles, but still strongly 
agglutinates them. 1 

Evidently the agglutination of the corpuscles 
and the setting free of the haemoglobin (termed 
"laking") are effected by different substances. 
The agglutinating body resists a temperature that 
destroys the blood-laking body. 

4. To the mixture used in the preceding experi- 
ment, add 2 c.c. of fresh serum from a normal 

1 A very slow destruction of the red corpuscles may be ob- 
served. This, however, is due to the fresh serum in the 1.5 c.c. 
defibrinated rabbit blood, as will be evident from Experiment 4. 



FERMENTATION 229 

guinea-pig (one that has not been injected with 
rabbit blood). 

In a few minutes the mixture becomes limpid 
and red. The laking power is restored. 

Obviously, with the fresh serum was added 
the unstable body destructive to red corpuscles. 
Ehrlich and Morgenroth have shown that at low 
temperatures the stable body unites with the red 
corpuscles while the unstable body remains in 
the serum ; in this case the haemoglobin is not 
set free. At higher temperatures the haemoglo- 
bin separates and the unstable body is found to 
have left the serum. It has joined the stable 
body in the sediment. 

Following the side-chain theory already men- 
tioned, Ehrlich and Morgenroth assume that the 
stable substance has two combining powers; 
on the one hand it unites with the red corpus- 
cles, on the other with the unstable substance, 
thus bringing it to the cell which it may then 
destroy. 

Immunity against toxin es and foreign red cor- 
puscles are only two of the protective actions of 
the blood. The injection of cells of the most 
varied kinds is followed by the production of 
specific protective bodies; 1 thus, the injection of 

1 Metehuikoff: Annales de l'lustitut Pasteur, 1900, xiv, 
p. 369. 



230 THE INCOME OF ENERGY 

bacteria causes the formation of bacteriolysines, 
which destroy the injurious organism. 

Many haemoly sines and agglutines are found 
in plants ; others, for example, the tetanus bacil- 
lus, are bacterial; still others, such as snake 
venom, are animal secretions. 

Oxidizing Ferments 

Schonbein's Experiment. 1 — 1. To five c. c. hy- 
drogen peroxide add tincture of guiac (freshly 
prepared by dissolving guiac resin in alcohol) 
drop by drop until the liquid is milky. Now 
add from eight to ten drops of a somewhat con- 
centrated extract of malt, prepared in the cold. 

The guiac will be oxidized and will turn blue. 

2. Eepeat the experiment, adding in place of 
the malt extract from eight to ten drops of blood. 

The guiac will be oxidized, as before. 

Further Oxidations by Animal Tissues. 2 - 1 — 
1. Soak strips of bibulous paper in a diluted solu- 
tion made as follows : 

a-naphthol 1 niol. 

sodium carbonate . . . .3 " 
para-phenylenediamine , . 1 " 

1 Schonbein : Zeitschrift fiir Biologie, 1868, iv, p. 367. 

2 Spitzer : Archiv fiir die gesaminte Physiplogie, 1895, ix, 
pp. 322-323. 



FERMENTATION 231 

This solution, left in the atmosphere, oxidizes 
slowly to indophenol (violet color). 

Place a drop of a known oxidizer, e.g. ferri- 
cyanide of potash or potassium bichromate, on 
the saturated paper. 

The color will change at once, in consequence 
of immediate oxidation. 

(1) C 6 H 4 (NH 2 ) 2 ;+ C 10 H 7 OH + O = 

PAKA-PHENYLENEDIAMINE A-NAPHTHOL CgH^NH^ 



NH< C 10 H 6 OH + ° - t < C M H.O +H2 ° 



INDOPHENOL 



Each of the combining molecules has been acted 
upon by a different oxygen atom ; hence the oxy- 
gen molecule must have been split. 

2. Rub the test paper with finely divided tissue 
from the liver or any other organ. 

Oxidation will occur. 

A drop of blood placed on the test paper is 
soon surrounded by a characteristically colored 
ring. 

Extraction of Nucleo-Proteid from Liver} — 
Perfuse a fresh liver (dog) with tap water until 
the washings are no longer colored by haemo- 

1 Spitzer : Archiv fur die gesamratc Physiologie, 1897, lxvii, 
p. 616. 



232 THE INCOME OF ENERGY 

globin. Grind the liver to a pulp and press 
through several thicknesses of gauze. Add five 
volumes of distilled water. Allow the mixture 
to stand twenty-four hours at low temperatures. 
Remove the opalescent watery extract with a 
pipette and filter through linen. Demonstrate 
with the microscope that liver cells are absent 
from the liquid. Add T %- HC1 drop by drop until 
there is no further precipitation, and the super- 
natant fluid is clear. Since the precipitate redis- 
solves in acid, use lacmoid as an indicator. Cease 
when the lacmoid shows a trace of excess. De- 
cant the precipitate, filter, wash the residue with 
water. 

Oxidation by Nucleo-Proteid. — Place in a wide- 
necked flask 50 c.c. water containing 0.2 gram 
of the fresh, brown substance and 10 c.c. hydro- 
gen peroxide in a small glass cup. The hydrogen 
peroxide must be neutralized with from 1 to 1.5 
c.c. ^ ? o NaOH. Connect the flask with the lower 
end of a eudiometer by means of a bent tube. 
Shake the flask so that the hydrogen peroxide 
shall come in contact with the tissue. Oxygen 
is at once set free. Eead in the eudiometer 
the oxygen developed from minute to minute. 
Spitzer found : 

After minutes .. 1234589 16 
C.c. 2 developed 19 28 41 55 69 85 87 95 



FERMENTATION 233 

Oxidation about the Nucleus. 1 — Introduce the 
oxidizable solution of a-naphthol and para-phe- 
nylenediamine (page 230), beneath the cover 
glass of a fresh preparation of teased thymus 
or spleen. 

"Granules of the intense greenish-blue oxi- 
dation product shortly make their appearance 
within the leucocytes. Their first appearance is 
typically at the boundary between nucleus and 
cytoplasm ; eventually the latter may become 
so densely laden as completely to obscure the 
nucleus. . . . The nucleus is the chief agency "in 
the intracellular activation of oxygen. The ac- 
tive or atomic oxygen is in general most abun- 
dantly freed at the surface of contact between 
nucleus and cytoplasm." 

Glycolysis in Blood. Bernard's Experiment? — 
125 c.c. dog's blood were divided into five equal 
parts. The sugar in each was estimated as 
follows : 











Sugar 
Grams per 1000. 


1. 


Analysis 


made afc once 


. 1.07 - 


2. 


a 


a 


after 10 minutes 


. 1.01 


3. 


a 


a 


"30 " ."'■' 


. 0.88 


4. 


a 


a 


" 5 hours . 


. 0.44 


5. 


it 


(C 


" 24 " 


. 0.00 



1 Lillie : American journal of physiology, 1902, vii, p. 420. 

2 Bernard : Comptes rendus de l'academie des sciences, Paris, 
1876, lxxxii, p. 1406. 



234 THE INCOME OF ENERGY 

Sugar disappears from the blood on stand- 
ing. 

It has been found by Lepine and Barral 1 that 
the glycolytic power of the blood increases as the 
temperature rises to 52.5° C, which is the opti- 
mum. At 54° the ferment is destroyed. 

Oxidation not Dependent on Living Cells of Blood. 
— Place the following solutions at 34-35° C. for 
six hours, allowing a stream of air to pass through 
the liquid. Then estimate the sugar. 2 

A. Calf's blood 100 c.c. 

Water containing 1.14 gram grape sugar 10 c.c. 
Seegen 3 recovered 1.000 gram. 

1 Lepine and Barral : Comptes rendus de l'academie des sci» 
ences, Paris, 1891, cxii, p. 146. 

2 Test the filtrate by adding a drop of acetic acid and a little 
ferrocyauide of potassium. 

The absence of a precipitate shows freedom from proteids and 
ferric salts. Concentrate filtrate to 150-200 c.c. 

Titration of the Sugar Extract. — Make the volume of the 
solution such that its probable content of sugar shall lie 
between 0.0004 and 0.0010.. Causse (Bulletin de la Societe 
chimique de Paris, 1, p. 625) recommends that 1750 c.c. of 
water containing 5 grams of ferrocyanide of potassium be added 
to each 250 c.c. of Fehling's solution. Boil 10 c.c. of this 
mixture and add the sugar solution drop by drop until the blu« 
liquid is decolorized (Arthus : Archives de physiologie, 1891, 
p. 425). 

3 Estimation of Sugar in Blood. Extraction of the Sugar 
from the Blood. — To 350-400 c.c. boiling water add all at once 
50 c.c. blood containing 5 c.c. one per cent acetic acid. Let 



FEKMENTATION 235 

B. Calf's blood 100 c.c. 

Water containing 1.14 gram grape sugar 10 c.c. 

Chloroform 1 c.c. 

Seegen recovered 0.960 gram. 

The chloroform destroys the cells, but fails to 
check the oxidation. 

Relation of Glycolysis to the Pancreas and the 
Lymph. 1 — Remove the pancreas aseptically from an 
anaesthetized dog which has fasted thirty-six hours. 
Estimate the sugar in the urine at intervals of a few 
hours. 

Sugar will be present in large and increasing quanti- 
ties, 2 rising even to twenty per cent. 

Inject into the jugular vein 15-20 c.c. of lymph 
from the thoracic duct of a dog fed a few hours before 
upon one litre of milk. 

the mixture boil for a few minutes. Filter through a small 
linen cloth. 

Separation of Proteids. — Boil the filtrate. Most of the pro- 
teids will separate by coagulation. The remainder, if necessary, 
may be removed by adding to each 300 c.c. of filtrate, 5 c.c. 
saturated solution of sodium acetate, and a small quantity of a 
dilute solution of ferric chloride, neutralizing almost completely 
with dilute soda solution, and boiling. The ferric chloride will 
precipitate as ferrous chloride and will carry down the last 
truces of proteid substances. Filter. Wash with boiling water. 
(Seegen : Centralblatt fur Physiologic, 1891, v, p. 824.) 

1 Lepine : Comptes rendus de l'academie des sciences, Paris, 
1890, ex, p. 742. 

2 Von Mering and Minkowski: Archiv fur experimentelle 
Pathologie und Pharmacologic, 1890, xxvi, p. 371. 



236 THE INCOME OF ENERGY 

The glycosuria will greatly diminish. 

After a few hours, the glycosuria will become once 
more intense, continuing until death. The quantity of 
sugar in the blood is also greatly increased. 

Glycolytic Ferment of Pancreas. 1 — Remove the 
pancreas aseptically from a dog immediately after 
death. Crush it at once in 100 c.c. sterile water 
containing 0.2 gram sulphuric acid. Allow it to 
macerate two hours at 38° C. Neutralize the 
acid with soda, add 0.5 gram pure glucose, and 
keep the mixture one hour at 38° C. Estimate 
the sugar. 

The loss will be from ten to fifty per cent. 

When pancreatic extract made without acid is used, 
the loss of sugar is much less. Probably, therefore, 
the glycolytic ferment is produced from a zymogen by 
hydration. 

Malt diastase, or salivary diastase, kept three hours 
at 38° in water containing one tenth per cent sulphuric 
acid loses the power to change starch to sugar, but ac- 
quires a glycolytic power. 

If the pancreatic juice which flows upon stimulation 
of the peripheral end of the vagus (Pawlow) is treated 
with dilute acid, 1 : 1000, the amylolytic power is lost, 
but glycolytic power is acquired. During the excita- 
tion of the nerve — while the juice is flowing — the 

1 Lepine : Comptes reiidus de l'academie des sciences, Paris, 
1895, cxx, p. 139. 



FERMENTATION 237 

blood in the pancreatic vein has almost no glycolytic 
power; after the juice ceases to run, the blood has 
considerable glycolytic power. Here the external is 
balanced against the internal secretion of the pancreas. 

Oxidative ferments are very widely distributed both 
in animals and plants. The above experiments show 
their presence in the blood, pancreas, liver, and lymph. 
They are present also in the urine. 

The stomach contains a ferment that oxidizes lactose 
to lactic acid. 1 

Urushi, the milky secretion of Rhus vernicifera, dries 
in the air to a translucent varnish (Japanese lacquer). 
It contains urushic acid, which does not dry sponta- 
neously, and a ferment, the addition of which to 
urushic acid causes the latter to dry to lacquer. A 
sample of fresh juice boiled to stop the action of the 
ferment on urushic acid contained 15.01 per cent 
oxygen ; lacquer dried in the usual maimer contained 
20.52 per cent oxygen. 

Many oxidations are effected by the tissues without 
the aid of ferments, so far as is yet known. These be- 
long properly to metabolism, but in passing, it may be 
noted that while substances exceedingly resistant to 
oxidation, for example, proteids, are oxidized in the 
body, other substances very easily oxidizable may be 
excreted unchanged ; oxalic acid is one of these. 2 



1 Hammarsten : Maly's Jaliresbericht der Thierchemie, 1S72, 
ii, p. 118. (Original in Swedish.) 

2 Pohl : Archiv fur experimentelle Pathologic und Pharraa- 
kologie, 1896, xxxvii, p. 413. 



238 THE INCOME OF ENERGY 

Hoppe-Seylers Theory* 1 — Living tissues consist of 
easily combustible reducing substances, which split 
the oxygen molecules, taking to themselves one atom 
of and setting the other free in active state to 
unite with any oxidizable substance present. 

Traube's Theory. 2 — In living protoplasm oxygen is 
rendered active by an oxidizing ferment, which brings 
the oxygen to bodies ordinarily oxidizable only by such 
powerful agents as heat and strong alkalies. 

Inorganic bodies, e. g. platinum black, the oxides of 
copper, silver, mercury, and vanadium, and certain iron 
salts similarly act as oxygen carriers. Thus 

(1) Pt + 2 + H 2 = PtO + H 2 

(2) PtO + H 2 = Pt + H 2 

The oxygen carrier reduces H 2 2 , takes one atom 
to itself, then gives off this atom in an active or 
nascent state to oxidize any , oxidizable compound 
present ; e. g. guiac. Grape sugar takes from 
indigo-blue, producing thereby indigo-white. The 
indigo-white oxidizes itself to indigo-blue, then gives 
up another atom of 0, and so on. 

Alcoholic Fermentation 
The Yeast Plant. — Observe a solution of sugar 
undergoing alcoholic fermentation. 3 Note the 
bubbles of gas, the scum, the sour odor. 

1 Hoppe-Seyler: Zeitsclirift fur physiologische Chemie, 1879, 
ii, p. 1. 

2 Traube : Berichte der deutschen chemischen Gesellschaft, 
1883, xvi, pp. 123, 1201, and earlier papers in volumes x and xv. 

3 The fermentation is assisted by providing the yeast plant 



FERMENTATION 239 

Examine some of the mixture under the micro- 
scope. Note the multitude of globular or slightly 
ovoid bodies, the largest about T £o mm. in diame- 
ter. They are motionless. Many have put forth 
buds. They seem to be plants in active growth. 1 

1. Place 300 c.c. of the nutrient liquid (Ex- 
periment 1) in a flask holding 500 c.c. Add a 
piece of fresh compressed yeast the size of a pea. 
Place the flask in a temperature of 35° C. 

Note that as fermentation advances the yeast 
increases in quantity. 

2. Place a small piece of fresh compressed 
yeast in a test-tube. Fill the tube with nutrient 
liquid and invert it in a dish of similar liquid. The 
tube may be kept upright by a clamp. Let the 
mixture stand twenty -four hours in a warm room. 

with the salts present in the ash of yeast (Pasteur). A useful 
substitute is 

Potassium phosphate ... 20 gms. 

Calcium phosphate ... 2 

Magnesium sulphate ... 2 

Ammonium tartrate . . . 100 

Cane sugar 1,500 

Water 8,376 

10,000 
(Practical biology, Huxley and Martin. ) 
1 Cagniard-Latour : L'lnstitut, 1835, iii, p. 150 ; also Annales 
de chimie et de physique, 1838, Ixviii, p. 206. The yeast plant 
was first observed microscopically in beer-yeast by Leeuwen- 
hoek, 1680, but he did not associate fermentation with thq 
growth of the yeast, 



240 THE INCOME OF ENERGY 

The tube will fill with gas. With a bent pipette 
introduce about 1 c.c. of a solution of sodium 
hydroxide (sp. gr. 1.12 = 11 per cent). The gas 
will be absorbed, with formation of sodic carbon- 
ate, and the liquid will rise in the tube. 

The growth of the yeast plant is accompanied 
by the production of carbon dioxide. 

3. Eeturn to Experiment 1. After the fer- 
menting liquid has ceased to give off gas, place a 
stopper with a bent tube in the mouth of the 
flask and distill the contents of the flask in a 
water bath. Condense the first fifth of the dis- 
tillate. Saturate this with sodium carbonate. 
Eedistill, and condense. 

Test for alcohol by warming the distillate with 
potassium dichromate and dilute sulphuric acid, 
whereby the alcohol will be oxidized to aldehyde, 
with characteristic odor. 

Alcohol is present. 

The production of alcohol by the yeast is the work 
of the ferment zymase. 1 This body is closely bound 
to the protoplasm of the cell, very easily destroyed, not 
produced in excess, and not secreted free. Only sugars 
containing three, six, and nine carbon atoms are at- 
tacked. The saccharobioses must be " inverted " be- 
fore they can be fermented. Thus, cane sugar must 

1 Buchner : Berichte der deutschen chemischen Gesellschaft, 
1897, xxx, pp. 117, 1110, 2668. 



FEEMENTATION 241 

first he inverted to grape sugar by invertin, 1 and 
malt sugar by maltase. Lactase is present in some 
yeasts, enabling them to ferment milk sugar. Diastase 
is also found. 

The action of these several ferments becomes clear 
when the chemical nature of the carbohydrates is 
recalled. 

Chemical Relations of Carbohydrates. — Carbohy- 
drates were formerly defined to be compounds con- 
taining six, or a multiple of six carbon atoms, together 
with hydrogen and oxygen atoms in the proportion in 
which they exist in water. The researches of E. 
Fischer have shown that all aldehydes (bodies which 
are the first oxidation products of primary alcohols, and 
which contain the carbonyl group CO) and all ketones 
(bodies which are the first oxidation products of second- 
ary alcohols and which likewise contain the carbonyl 
group CO) contain carbon, hydrogen, and oxygen, there 
being two atoms of hydrogen to one atom of oxygen, 
as in water. 

The carbohydrates, therefore, no longer occupy an 
isolated position, but are to be classed with the fats, 
being methane derivatives in which the carbon atoms 
are arranged in an open chain; thus, grape sugar is an 
aldehyde alcohol, and fruit sugar a ketone alcohol. 

The carbohydrates are divided, according to the size 
of their molecule, into monosaccharides, disaccharides, 
and polysaccharides. The monosaccharides (e. g. grape 

1 For extraction, see Lea : Journal of physiology, 1SS5, vi, 

p. 142. 

16 



242 



THE INCOME OF ENERGY 



sugar) are the first oxidation products of the hexahy- 
dric alcohols ; the higher carbohydrates are anhydrides 
of the monosaccharides. Most of the higher carbohy- 
drates cannot be fermented directly, but must first 
be hydrolyzed (i. e. take up water). This hydrolysis 
may be accomplished by the prolonged action of dilute 
acids at high temperatures, by the action of water at 
still higher temperatures, or by specific ferments, e. g. 
diastase, at the relatively low temperature of the body. 
The polysaccharides, consisting of the starches, the 
gums (e. g. dextrine or starch gum) and the celluloses 
(wood fibre) differ greatly from the lower carbohy- 
drates. The polysaccharides are usually amorphous 
and are not easily soluble in water. 



Carbohydrates. 1 



Glucoses, Monoses 
C 6 H 12 6 . 


Saccharobioses 
C12H22O11. 


Polysaccharides 

(C 6 H 10 O 5 )x. 


Grape sugar — 


-Malt sugar — 


— Starch 




Grape sugar — 


-' 






Grape sugar — 
Fruit sugar — 


-Cane sugar 






Grape sugar — 


-Milk sugar 






Galactose — 

















1 Richter's Orgairic Chemistry, Third American Edition, i, 
p. 121. 



FERMENTATION 243 

The zymase attacks only those sugars which present 
a specific stereo-configuration. The position of their 
atoms in space must fit the position of the atoms of 
the ferment (the lock and the key). Thus, only the 
dextro-rotatory forms of the aldehyde sugars (d-glu- 
cose, d-mannose, d-galactose) are attacked ; the sugars 
that rotate the plane of polarized light to the left 
are not attacked. It is probable that the zymase 
of different species of yeast presents characteristic dif- 
ferences. It is known that the products formed in the 
fermentation of sugar by different species of yeasts are 
to a large degree characteristic. Often these products 
are injurious. Upon this specific action of ferments 
rests the work of Hansen, 1 who taught the brewers to 
make pure cultures of the most favorable species of 
yeast, and thereby raised the brewing industry to the 
level of an applied science. 

Activating Ferments 

Enterpkinase. — In 1899, Chepowalnikow, 2 in 
Pawlow's laboratory, found that pancreatic juice 
obtained by Pawlow's 3 method contained very 

1 Hansen : Untersuchungen an der Praxis der Gahrungs- 
Industrie, 1895. 

2 Chepowalnikow : Thesis (Russian), St. Petersburg, 1899, 
Paris, 1901. 

3 In Pawlow's method the intestine is resected and the 
portion of the intestinal wall containing the opening of the 
pancreatic duct is stitched to the edges of the abdominal wound, 
where it soon unites ; the pancreatic duct then discharges upon 
the surface of the abdomen, where the juice may be caught by 
applying a suitable vessel. 



244 THE INCOME OF ENERGY 

little trypsin and had a correspondingly slight 
action on proteids. When intestinal juice was 
added to this pancreatic juice, the pancreatic 
juice at once became active in proteid digestion. 
Pawlow called the activating body enterokinase. 1 
In 1902, Delezenne and Frouin 2 found that 
pancreatic juice obtained by catheterizing the 
pancreatic duct contained no trypsin whatever; 
their procedure prevented any contact between 
the juice and the intestinal mucous membrane 
at the orifice of the pancreatic duct. It has been 
shown that enterokinase is a ferment, secreted 
in the small intestine, and that it converts tryp- 
sinogen contained in pure pancreatic juice into 
trypsin, the active proteid ferment. 

Preparation of Ejiterokinase. — Scrape lightly 
with the handle of a scalpel the upper part of 
the mucous membrane of the small intestine 
(dog or cat). Digest the scrapings during two 
days in a closed vessel of water to which a few 
drops of chloroform have been added to prevent de- 
composition. Filter through paper, then through 
a Berkefeldt filter. The resulting solution is 
perfectly clear, contains a certain amount of 
coagulable proteid, and will retain its activity 

1 Pawlow : The Work of the Digestive Glands, translated 
by W. H. Thompson, 1902, p. 160. 

2 Delezenne and Frouin : Comptes rendus de la societe 
de biologie, Paris, 1902, pp. 691-693. 



FERMENTATION 245 

at room temperature for many months. It is 
rapidly destroyed at 35°-40° C. 1 

Conversion of Trypsinogen to Trypsin by En- 
terokinase. — Place 5 c.c. of 0.25 per cent solution 
of sodium carbonate in each of two test-tubes 
A and B, containing gelatine prepared by Fermi's 2 
method. To A add a few drops of pure pancreatic 
juice ; 3 to B add the same quantity of pure pan- 
creatic juice and a few drops of enterokinase. 
Place at a temperature of 30°-35° C. The pure 
juice will not act on it, but the juice to which 
enterokinase was added will dissolve the gelatine. 
In order to determine accurately the amount of 
gelatine dissolved, the tubes often must be cooled 
to 10° C. 

Absorption of Proteids 

Diffusion of Proteids through Dead Membrane. 

— Bend a cylinder of parchment paper and fasten 
the ends to a glass rod. Place in the parchment 
tubes thus formed 25 c.c. of each of the follow- 

1 Bayliss and Starling: Journal of Physiology, 1903, 
xxx, p. 80. 

2 Fermi and Repetto : Centralblatt fur Bakteriologie mid 
Parasitenkunde, 1902, xxxi, p. 404. Narrow glass tubes, pref- 
erably graduated, are rilled one half full of gelatine (5 to 10 
per cent) containing one per cent of sodium fluoride. 

3 Obtained by catheterizing the pancreatic duct of the rabbit 
(Rachford's method), Journal of Physiology, 1891, xii, p. 81. 



246 



THE INCOME OF ENERGY 



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FERMENTATION 



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248 THE INCOME OF ENERGY 

ing solutions : 1 (1) Egg-albumin, (2) Myosin, (3) 
Alkali-albumin, (4) Peptones. Suspend the egg- 
albumin and the peptone in vessels containing 
one litre of normal saline solution (0.8 per cent 
sodium chloride) ; the alkali-albumin in one litre 

1 Preparation of egg-albumin. — Thoroughly mix the whites 
of twelve or more eggs with saturated solution of magnesium 
sulphate at 20° C. Filter from the precipitated globulin. 
Saturate the filtrate at 20° C. with sodium sulphate. Filter 
the precipitated albumin. Press in filter paper. Dissolve in 
water. Dialyse until the dialysate is free from sulphates. 
(Starke, quoted by Hammarsten : Lehrbuch der physiologischen 
Chemie, 1897, p. 372.) Determine the albumin in a measured 
quantity of the solution, as follows. 

Quantitative Estimation of Egg -albumin. — To 25 c.c. of the 
albuminous liquid add an equal quantity of 4 per cent sodium 
chloride solution. Neutralize exactly. Boil 5 c.c. of this mix- 
ture in a test-tube. To the boiling liquid add one drop of acetic 
acid from a burette. Filter from the precipitated proteid. Pour 
the filtrate carefully down the side of a conical glass containing 
about 5 c.c. concentrated nitric acid, so that the lighter liquid 
rests on the heavier acid. If the surface of separation remain 
clear, all the albumin in the 5 c.c. was precipitated by adding 
to the boiling liquid one drop of acetic acid. If a white ring 
form, albumin is still present (Heller's test). In this case boil 
a fresh portion (5 c.c), add two drops acetic acid, filter, and 
test the filtrate. Determine in this way how much acetic acid 
must be added to each 5 c.c. of the albuminous liquid to pre- 
cipitate all the albumin when the liquid is boiled. Heat 25 c.c. 
of the remaining portion of the albuminous liquid in a water 
bath. Add slowly with constant stirring the calculated quan- 
tity of acetic acid. Heat ten minutes longer. Filter through 
weighed paper. Test filtrate once more for albumin. If none be 
present, wash with water, alcohol, and ether, dry at 40°, weigh, 



FERMENTATION 249 

of 0.1 per cent sodium carbonate solution ; and 
the myosin in one litre of 5 per cent sodium 
chloride solution. 

After three hours determine the amount of 

subtract the weight of the filter. There remains the weight of 
the albumin in 25 c.c. of the original solution. 1 

Preparation of Myosin. — Use muscle containing little blood 
(calf, rabbit, fowl, frog). Hash the muscle. Wash with water 
until the washings are free from proteid. Remove excess of 
wash water by pressure. Mix with enough 15 per cent solu- 
tion of ammonium chloride to cover the mass. After four hours, 
filter through cloth and then through paper. The filtrate should 
be clear, opalescent, somewhat thick. Dialyse in running water. 
As the neutral salt is removed, the myosin will separate in fine 
flocks (Danilewsky). Redissolve in 5 per cent sodium chloride 
solution. 

Quantitative Estimation of Myosin. — Dialyse 25 c.c. of the 
saline solution of myosin until the dialysate is free from salt. 
Wash the precipitated myosin into a tall narrow beaker. When 
the myosin has settled, decant as much of the supernatant liquid 
as possible. To the remainder add alcohol in such proportion 
that the mixture shall contain 80 per cent. After coagulation, 
filter through a weighed filter. Wash with alcohol and ether. 
Dry at 100°. Weigh. Subtract the weight of the filter. 

Preparation of Alkali-albumin. — Warm the whites of twelve 
or more eggs with 1 per cent sodium hydrate at 40° C. Filter. 
Neutralize very cautiously with hydrochloric acid, at first 1 per 
cent, later 0.1 per cent. The alkali-albumin will be precipi- 
tated. Allow to stand several hours. Filter. Boil the filtrate. 
Filter from the fresh precipitate and add residue to first pre- 

1 Literature. — Kuhne: Untersuchungen iiber das Protoplasm;!, 1864, 
p. 2. Danilewsky : Zeitschrift fur physiologische Chemie, 1SS1, v. p. 158. 
Halliburton: Journal of Physiology, 1S87, viii, p. 132. Kuhne and 
Chittenden : Zeitschrift fur Biologie, 1889, xxv, p. 358. 



250 THE INCOME OF ENERGY 

proteid in each tube and state the per cent that 
has passed through the membrane. 

Diffusion through Living Intestinal Wall. 1 — 
Through a small opening in the linea alba of a 
fasting anaesthetized cat 2 draw out a loop near 
the middle of the small intestine. Eemove the 
contents by careful stroking. Tie double liga- 
tures 0.5 cm. apart around the intestine at one 
end of the loop and similar ligatures at a point 
30 cm. from the first pair. With a hypodermic 

cipitate. 1 Wash with water. Redissolve in water containing 
0.1 per cent sodium hydrate. 

Quantitative Estimation of Alkali- albumin. — Neutralize a 
measured quantity of the solution. Separate the neutralization 
precipitate upon a weighed filter. Wash with water, alcohol, 
and ether. Dry and weigh. 

Preparation of Peptones. — The separation of peptone from 
the albumoses 2 with which it is obtained in the tryptic diges- 
tion of proteids is so difficult that it should not he attempted 
in these experiments. Add commercial peptone, often contain- 
ing albumoses as an impurity, to a small quantity of boiling 
neutral distilled water. Filter. 

Quantitative Estimation of Peptone. — To 10 c.c. of the liquid 
add alcohol in such proportion that the mixture shall contain 
80 per cent. Filter through weighed filter paper. Dry at 
40° C. Weigh. [This method is not exact, but is to be pre- 
ferred for the purpose in hand.] 

1 Voit and Bauer : Zeitschrift fiir Biologie, 1869, v, p. 562. 

2 These and subsequent operations will be done by an in- 
structor assisted by a committee of the class. 

1 Hawk and Gies : American Journal of Physiology, 1902, vii, p. 460. 

2 Kuhne : Zeitsclirift fur Biologie, 1892, xxix, p. 1. 



FEEMENTATION 251 

needle attached to a burette inject into the 
loop sufficient egg-albumin solution to distend it 
slightly. Measure the volume of the solution 
injected. The content of this solution was found 
in the course of the experiment on diffusion 
through dead membranes (page 245). 

Eeplace the loop in the abdomen. At some 
distance from this loop prepare a control loop 
with double ligatures in the same way, but leave 
the control loop empty. Sew up the abdominal 
wound. 

After three hours, kill the animal (best by 
puncture of the spinal bulb). Eemove the loops 
by cutting between the double ligatures. Eapidly 
wash the outer surface with water, dry the sur- 
face with filter paper, open the loops, measure 
the volume of the contents, wash the inner sur- 
face, add the washings to the contents, and 
estimate the proteid in a measured portion. 

Perform a similar experiment with solutions of 
(2) myosin, (3) alkali-albumin, and (4) peptone. 

Compare the results of absorption of proteids 
through the living intestinal wall with absorp- 
tion through dead membranes. It will appear 
that the living cells of the intestinal wall modify 
absorption so that it does not follow the law of 
diffusion through dead membrane. 

It is also evident that egg-albumin, myosin, 



252 THE INCOME OF ENERGY 

alkali-albumin, and peptone may be absorbed 
unchanged. Indeed, the absorption of alkali- 
albumin is almost or quite as complete as that 
of peptone. The conversion of proteids to 
peptones is advantageous but not essential to 
absorption. 

Absorption Velocity Compared -with Diffusion 
Velocity. 1 — Prepare a cat as in Experiment 2. 
Fill one intestinal loop with a measured quantity 
of 5 per cent dextrose solution, the other with 
0.25 per cent solution of sodium sulphate. After 
one hour kill the animal, measure the liquid re- 
maining in the two loops and estimate its content 
in dextrose and sodium sulphate respectively. 2 

The dextrose solution will be found to have 
been largely or completely absorbed, w T hile rela- 

1 Rohmaxn: Archiv fur die gesammte Physiologie, 1887, 
xii, p. 456. 

2 The quantitative estimation of dextrose is described in 
"Experiments for Students in the Harvard Medical School," 
third edition, p. 38. 

Quantitative Estimation of Sodium Sulphate. — Boil the solu- 
tion, make the reaction acid with a few drops of hydrochloric 
acid, add hot solution of barium chloride in slight excess (until 
barium sulphate ceases to be precipitated). Boil a few minutes. 
Wait for the precipitate to settle. Decant the clear liquid 
through a filter, the ash of which is of known weight. Boil the 
precipitate in the beaker repeatedly with water. Place the pre- 
cipitate on the filter. Wash with boiling water. Dry. Heat to 
redness in a weighed crucible. Weigh when cold. (The atomic 
weights are: barium, 137.4; sulphur, 32.06; oxygen, 16.) 



FERMENTATION 253 

tively little of the sodium sulphate will have 
left the intestine. Yet sodium sulphate is some- 
what more diffusible than dextrose. 1 

Assimilable Proteids. — With a catheter re- 
move the urine from the bladder of an anaesthe- 
tized female cat, and apply Heller's test for 
albumin (page 248). Albumin should be absent. 
Slowly inject into the jugular vein 25 c.c. of 
solution of alkali-albumin (page 249) at the tem- 
perature of the body. Test the urine for albumin 
twice, at intervals of half an hour. 

No albumin will be found. The alkali- albumin 
has not been removed from the blood by the 
kidneys. 

Non- Assimilable Proteids. — Perform a similar 
experiment on another cat, injecting solution of 
egg-albumin instead of alkali-albumin. 

Albumin will be found in the urine. Egg- 
albumin, present in the blood, is at once re- 
moved by the kidneys. It cannot be used unless 
changed ("digested") in the intestine. 2 Albu- 
moses and peptones are also non-assimilable; 
they produce a dangerous fall in blood-pressure. 

1 Compare Hoffmann: Eckhard's Beitrage zur Anatomie 
und Physiologie, 1860, ii, p. 65. 

2 Munk, J., and M. Lewandowsky (Archiv fur Physiologie, 
1899, Supplement, pp. 73-88) find the non-assimilable proteids 
of Neumeister ( not including albumoses and peptones) may be 
assimilated if injected very slowly into the blood. 



254 THE INCOME OF ENERGY 

Alimentary Albuminuria. — Test the urine of a 
human subject for albumin at half-hour intervals. 
After the first test let the subject swallow the 
whites of six raw eggs. 

Albumin will probably be found. In many 
subjects a portion of any unusual quantity of 
egg-albumin may be absorbed unchanged into the 
blood, whence it is removed by the kidneys. 

Albumose and Peptone not ordinarily Present 
in the Blood or Urine. — Dissolve as completely 
as possible ten grams of commercial peptone, 
which contains albumose as an impurity, in a 
small quantity of water. Boil. Filter. Measure 
the filtrate. 

Through a small opening in the linea alba of a 
fasting anaesthetized cat draw out a loop near the 
middle of the small intestine. Remove the con- 
tents by careful stroking. Tie double ligatures 
0.5 cm. apart around the intestine at one end of 
the loop and similar ligatures at a point 30 cm. 
from the first pair. With a hypodermic needle 
inject into the loop sufficient peptone solution to 
distend it slightly. Measure the amount injected. 
Replace the loop in the abdomen and close the 
wound. Keep the animal in a cage arranged to 
collect voided urine. 

After two hours,, withdraw the urine from the 
bladder and add it to any that may have been 
spontaneously voided. 



FERMENTATION 255 

Bleed the animal from the carotid artery, re- 
ceiving the blood into an equal volume of satu- 
rated solution of ammonium sulphate, to prevent 
coagulation. Remove the intestinal loop by cut- 
ting between the double ligatures. Measure the 
liquid remaining in the intestine. It will be 
found that most of the peptone has disappeared. 
Test the blood and the urine for peptone 1 

1 Recognition of Peptone in Blood. — To the blood already- 
mixed with an equal volume of ammonium sulphate solution 
add crystals of ammonium sulphate to saturation. Filter from 
the precipitated proteids. To the clear filtrate apply the biuret 
test for peptone. 

Biuret reaction. — To the saturated ammonium sulphate 
nitrate add half its volume of saturated solution of potassium 
hydrate. Shake the dense precipitate. Allow the tube to 
stand two or three minutes until the heat developed by the 
chemical action passes off. Add a drop of very dilute solution 
of cupric sulphate. The fluid, dense white from the precipitated 
salts, assumes a pale blue color, due to the solution of hydrated 
cupric oxide in the ammonia generated. The same quantity of 
saturated potassium hydrate as before is now allowed to flow 
down the tube, and to form a layer at the bottom. If peptone 
is present a rose red ring is formed at the junction of the two 
layers. The contrast of the red ring with the pale blue above 
it renders the test very delicate (Neumeister's method modified 
by Shore : Journal of Physiology, 1890, xi, pp. 532-534). 

Recognition of Peptone in Urine. - — Remove the coloring 
matter by (1) adding solid lead acetate and filtering from the 
heavy precipitate ; (2) adding to the filtrate ammonium sul- 
phate, and filtering from the copious precipitate of lead sulphate ; 
(3) saturating the filtrate with crystals of ammonium sulphate 
and filtering from the additional precipitate. On filtration the 



256 THE INCOME OF ENERGY 

with the biuret reaction. No peptone will be 
found. 1 

An examination of the lymph would show 
that it also contains no peptone. Apparently 
the peptone absorbed from the intestinal loop is 
changed in its passage through the intestinal 
wall. This conclusion is made secure by the ex- 
periments of Salvioli, 2 who removed the jejunum 
of the dog or rabbit, tied a cannula in the mesen- 
teric artery and vein, and established through 
these vessels an artificial circulation of defibri- 
nated blood diluted with isotonic saline solution. 
One gram of peptone was dissolved in 10 c.c. of 
normal saline solution and placed in the intes- 
tine, and the artificial circulation maintained four 
hours. The peptone disappeared from the intes- 
tine, but none could be found in the blood. 

Albumose and Peptone changed in their Passage 
through the Intestinal Wall. — Kill a fairly large 
anaesthetized rabbit by bleeding. Beat the blood 

solution is free from lead, but usually still contains a trace of 
yellow pigment. Apply the biuret reaction as above. If the 
urine requires to be concentrated, it is better to evaporate the 
final ammonium sulphate filtrate, as boiling the urine at first 
deepens the color. (Neumeister and Shore, loc. cit.) 

1 Neumeisteb, : Zeitschrift fur Biologie, 1888, xxiv, pp. 
278-279. 

2 Salvioli : Archiv fur Physiologie, 1880, Supplemental 
volume, p. 112. 



FERMENTATION 257 

until all the fibrin separates. Filter through 
gauze into a cylinder holding 100 c.c. To the 
30 c.c. defibrinated blood add 30 c.c. sodium 
chloride solution (0.5 per cent) containing 0.6 
gram salt-free peptone. The mixture will thus 
contain 1.0 per cent of peptone. Reserve 5 c.c. 
of the mixture. Place the rest in a half-litre 
flask, provided with a stopper pierced by two 
glass tubes, one reaching to near the bottom 
of the flask, the other ending just beneath the 
stopper so that air may be drawn through the 
blood-peptone solution by an aspirator. Place 
the flask in a beaker with a heavy iron ring 
around the neck to prevent the flask being driven 
upward, fill the beaker with water at 40° C. and 
place it in a water bath also at 40°. 

Separate the intestine carefully from the mes- 
entery and especially the pancreas. Slit the 
intestine from the pylorus to the ilio-csecal valve 
with scissors, cut it into several pieces, wash it 
in a large water-bath filled with 0.5 per cent 
sodium chloride solution at 40° C. Repeat the 
washing in a second and a third bath. Cut the 
intestine into finger-lengths. Collect the pieces 
on a porcelain sieve, wash them with 1 per cent 
peptone solution, and then place them in the 
blood-peptone solution. Draw air through the 
solution, with every possible care against foam- 

17 



258 THE INCOME OF ENERGY 

ing. These several operations, beginning with 
the bleeding of the rabbit, should take not more 
than fifteen minutes. 

After two hours interrupt the experiment, 
pour the solution through a sieve, stir into the 
filtrate solid ammonium sulphate to saturation, 
filter off about 10 c.c., add to the water-clear fil- 
trate an equal volume of absolute sodium hydrate 
(70 per cent), stir thoroughly with a glass rod, 
and let the precipitated sodium sulphate settle. 

Add to the clear liquid drop by drop 2 per 
cent cupric sulphate solution. No biuret reaction 
will be obtained, but the liquid will show at once 
a pure blue color. 

Kepeat the test, with the same quantitative 
relations, upon the reserved 5 c.c. of the blood- 
peptone solution : a purple color will be obtained. 

Hence the not inconsiderable quantity of pep- 
tone in the blood covering the pieces of intestine 
has disappeared. 

Eub the pieces of intestine with sand to a 
pulp, boil with as little water as possible, saturate 
with ammonium sulphate, and test as before. 

No biuret reaction will be obtained. Hence 
the peptone which disappeared from the blood- 
peptone solution is not stored in the intestine. 1 

1 Neumeister : Zeitschrift fur Biologie, 1890, xxvii, pp. 324- 
327. 



FERMENTATION 259 

Cohnheim 2 attempted to find in the intestinal 
wall the peptone which disappears from the 
intestine without entering the intestinal blood 
and lymph. His failure led him to the dis- 
covery of a new ferment Erepsin (ipei7rco, I de- 
stroy), the action of which is to split peptone into 
crystallizable substances. This ferment, which is 
found in many tissues, was isolated by fractional 
precipitation with ammonium sulphate. Two 
parts of intestinal extract were mixed with three 
parts of concentrated ammonium sulphate. The 
resulting thick precipitate, consisting largely of 
proteid was dialyzed, and the erepsin found in 
the dialysate. 

The disappearance of peptone from the intes- 
tine is probably therefore not to be explained by 
the assimilation of the peptone or its reconver- 
sion into other forms of proteid, but by the split- 
ting of the peptone through the action of the 
ferment erepsin. 

Absorption of Fats, Fat Acids, and Soaps 2 

Absorption of Fat. — 1. Place a few drops of 
neutral olive oil in the pharynx of a frog that 

1 Cohnheim : Zeitschrift fur physiologische Chemie, 1901, 
xxxiii, pp. 451-465. 

2 Will : Archiv fur die gesammte Physiol ogie, 1879, xx, 
pp. 255-262. These experiments are best performed upon 
summer frogs, i. e. not during the normal period of hibernation. 



260 THE INCOME OF ENERGY 

has fasted at least fourteen days. After about 
twenty-four hours, remove the intestine and im- 
merse it from thirty to forty minutes in 0.25 per 
cent osmic acid solution. 1 

Slice the epithelial layer from its base. Tease 
on a glass slide and examine under the micro- 
scope. 

Particles of fat stained deep-brown by the osmic 
acid will be found in the epithelial cells. 

In a " control " frog that has fasted fourteen 
days, show that the intestinal epithelium is free 
from fat. 

2. Open the stomach of a frog the brain and 
spinal cord of which have been destroyed. Tie 
a glass cannula in the pylorus. Tie a ligature 
around the lower end of the intestine. Kemove 
the intestine. Place about 1 c.c. normal saline 
solution in a test-tube. Hang the intestine in 
the test-tube by passing the cannula through 
the cork. Place a little neutral olive oil in the 
intestine. After about twenty-four hours stain 
the epithelium with osmic acid and examine as 
before. 

Drops of fat will be found in the cells, but the 

1 Preparation of Osmic Acid Solution. — The glass capsule 
containing a known quantity of osmic acid is placed in a bottle 
and enough water is then added to make the required solution. 
The capsule is then broken. [The vapor of osmic acid is very 
irritating. ] 



FERMENTATION 261 

quantity absorbed will be less than in the living 
animal. 

3. Kepeat Experiment 2, using an emulsion of 
commercial olive oil and 0.25 per cent solution of 
sodium carbonate. 

Absorption will be increased by the giving of 
the fat in an emulsion. 

Absorption of Fat Acids. — Place in the pharynx 
of a frog a pill of pure palmitic acid made with a 
few drops of glycerine. After about twenty-four 
hours examine as before. 

Numerous drops of fat will be found in the in- 
testinal epithelium. These globules are not free 
fat acid absorbed as emulsion, for miscrocopic 
examination of the contents of the intestine 
shows no emulsion. Moreover, palmitic acid 
must be liquid to be emulsified, and as its melt- 
ing-point is 62° C. it could not melt in the 
intestine of a cold-blooded animal at room tem- 
perature. 

Absorption of Fat Acid as a Soap. 1 — Feed a 
frog with palmitin soap containing a few drops of 
glycerine. After about twenty-four hours exam- 
ine the intestine for fat, as before. 

1 Preparation of Palmitin Soap. — Dissolve ten grams pure 
palmitic acid in hot alcohol. Add enough 5 per cent potassium 
hydrate to combine with the fat acid. Drive off the alcohol 
by heating on a water-bath. Dilute with water and add a few 
drops of glycerine. 



262 THE INCOME OF ENERGY 

Fat globules will be found in the epithelial 
cells. 

Lymph 

Permeability of Vessel Wall in Inflammation. 

— 1. In a curarized frog whose brain has been 
destroyed by pithing spread the mesentery over 
the glass plate of the mesentery board, and ob- 
serve the capillary circulation under the micro- 
scope. Note the following changes. Dilatation 
of the arteries, veins, and capillaries, in the order 
named. With the dilatation an increase in the 
speed of the blood-stream, most noticeable in 
the arteries. After half an hour to an hour the 
acceleration gives place to slowing. All the 
vessels are now dilated, many capillaries are 
plainly visible that could hardly be made out in 
the normal state, the pulsation in the arteries 
is uncommonly strong down to their smallest 
branches, yet the circulation is everywhere slug- 
gish. In consequence of the slow blood-stream, 
the capillaries become crowded with corpuscles, 
so that they appear redder and more volumi- 
nous than normal, yet their cross-section is only 
slightly increased. In the veins the normally 
almost clear plasma next the wall fills gradually 
with leucocytes. The white corpuscles pass 
through the walls of the veins and capillaries. 



FERMENTATION 263 

Bed corpuscles escape from the capillaries. 
Hand in hand with the extravasation of cor- 
puscles, there is an increased transudation of 
lymph. The tissue swells with lymph, which 
soon exudes upon the free surface of the mes- 
entery, where it clots. The surface is then 
covered with a fibrinous membrane, crowded 
with white corpuscles, and containing also some 
red corpuscles. 1 

2. Place on the frog's tongue a small drop of 
croton oil mixed with fifty times its volume of 
olive oil. After thirty seconds wipe off the 
croton oil. Observe the inflammatory process 
under the microscope. 

3. Place a rubber band around the base of a 
white rabbit-ear and thus interrupt the venous 
flow. Hold the tip of the ear in warm water 
until it has a temperature of about 44° 0. 
Take the ear from the water and remove the 
band. 

Note the rosy swelling (oedema with slight 
extravasation of blood-corpuscles) in the in- 
flamed area. 2 

1 Cohnheim : Allgemeine Pathologie, 1882, i, pp. 237-241. 

2 Id.: Loc. cit., pp. 244-245. 



264 THE INCOME OF ENERGY 
II BLOOD 

Specific Gravity 

Drawing the Blood. — Wash the lobe of the ear 
with a bit of absorbent cotton dipped in clean 
water. 1 Eub the lobe dry with another piece 
of cotton. Pass a three-sided surgical needle 
through a Bunsen flame. (Do not heat the 
needle red or the temper will be drawn and the 
sharpness lost.) Stretch the skin of the lobe 
between the fingers of the left hand. Make a 
quick puncture one-eighth inch deep in the edge 
of the lobe. Press gently to start the flow. The 
blood must now flow freely. On no account use 
blood squeezed out. 

Determination of Specific Gravity. 2 — Fill a 
small beaker half full of a mixture of benzol and 
chloroform of a specific gravity of about 1059. 
Let a drop of the blood fall into this mixture. 
The drop will remain spherical, for blood does 
not mix with benzol and chloroform. If the 
drop sinks, add chloroform drop by drop, mean- 
while stirring the mixture with a glass rod, until 

1 Subjects who are " bleeders" are not to be used for this 
observation. 

2 Roy: Journal of Physiology, 1884, v, p. ix. Ham- 
merschlag, A. : Wiener klinische Wochenschrift, 1890, iii, 
p. 1018. 



BLOOD 265 

the drop neither rises to the surface nor sinks 
to the bottom but swims with the mixture. If 
the drop rests upon the surface, add benzol in 
a similar manner. When the drop neither sinks 
nor floats, its specific gravity must be that of the 
benzol-chloroform mixture. Pour the mixture 
into a glass cylinder, through a piece of linen to 
hold back the blood-drop, and take the specific 
gravity of the benzol-chloroform with an areom- 
eter. The result is also the specific gravity of 
the blood. 

The values obtained are slightly too low. The 
error is one unit in the third decimal place. 

Determine the specific gravity of the blood 
under the following conditions. Eecord the re- 
sults in the laboratory note-book. Hand to the 
instructor a copy of your observations written in 
ink upon a laboratory blank. The material col- 
lected by the class will be analyzed statistically 
by a committee and a report made. 

1. The specific gravity of the blood in a healthy 
man. 

2. In the same man half an hour after drink- 
ing 750 c.c. of water. 

3. In the same man one hour after drinking 
750 c.c. of water. 

4. In the same man after profuse sweating. 
Note any feeling of thirst. 



%66 THE INCOME OF ENERGY 

5. In a health j woman. 

Hammerschlag found the specific gravity in 
chlorosis and nephritis diminished as the haemo- 
globin diminished. No relation was observed 
between the appearance of oedema and a reduc- 
tion in the specific gravity. 

Counting the Corpuscles 

Counting the Red Corpuscles. — See that the 
pipettes of the Thoma-Zeiss apparatus are per- 
fectly clean and dry. Open the bottle contain- 
ing Gower's solution (sodium sulphate, 7.3 grams ; 
acetic acid, 20 c.c. ; water, 125 c.c). Prick the 
ear as directed on page 264. In a large drop 
which has collected without pressure put the 
point of the smaller Thoma-Zeiss pipette ( " red 
counter " ). Fill the pipette to the mark 0.5" by 
careful suction. Should the mark be passed, 
lower the column to the mark by touching the 
point of the pipette to filter paper. When the 
mark is reached, clean the outside of the pipette, 
dip the end in Gower's diluent solution, and 
draw the liquid very carefully up to the mark 
101. (Should the liquid pass the mark, the 
pipette must be cleaned and dried and the whole 
process repeated.) Close the ends of the pipette 
with the fingers, and shake it gently for one 



BLOOD 267 

minute in order to mix the blood thoroughly 
with the diluent. The blood will now be diluted 
200 times its volume. 

Eemove the rubber tube from the pipette. 
Blow out the unmixed solution in the capillary 
tube, between the point and the bulb, and several 
drops of the mixture in the bulb. Wipe off the 
end of the pipette. Touch it to the ruled disc. 
Let a very small drop flow out. Place the cover 
glass on the drop. The flattened drop should 
almost cover the glass. If it spread into the 
moat, clean the disc and use a second, smaller 
drop. If Newton's color-rings cannot be seen 
between the cover-glass and the disc by placing 
the eyes near the level of the cover-glass, another 
preparation must be made, with cleaner disc and 
cover-glass. 

Use Leitz No. 5 or Zeiss D objective. Bring 
the drop into focus and then, using the microm- 
eter screw, find the ruled field. 

On the central portion of the disc 1 square 
millimetre has been ruled into 400 squares, each 
square having therefore an area of ^-j-^- square 
millimetre. Each 16 small squares are sur- 
rounded by double lines, thus forming a " large 
square." In the Zappert-Ewing slide, the cen- 
tral square of 1 mm. is surrounded by eight other 
squares of 1 mm. each, and the central ruling is 



268 THE INCOME OF ENERGY 

extended through the surrounding squares, which 
are intersected by lines \ mm. apart. Count the 
number of corpuscles, square by square, in 200 
small squares. Corpuscles touching the north 
and south lines of each area are to be counted 
in, those touching the east and west lines are to 
be omitted from the count. 

Each square has an area of ? i_ square milli- 
metre. The thickness of the layer of blood, i. e. 
the distance from the ruled disc to the cover- 
glass, is 0.1 mm. The volume of the space above 
each square, therefore, is 4 oVo cu °i c millimetre. 
As the blood is diluted 200 times its volume, and 
the number of squares counted is 200, the total 
number of corpuscles in a cubic millimetre is 
x X 200 x 4000 
200 
x being the total number of corpuscles counted. 
In short, to obtain the number of corpuscles in a 
cubic millimetre, multiply by 4000 the number 
counted in 200 squares. Clean the pipette as 
soon as the counting is done. 

Cleaning the Pipette. — Draw clean Gower's 
solution through the pipette, then alcohol, and 
finally ether. Dry the pipette by sucking (not 
blowing) air through it. 1 

1 Do not use alcohol and ether in cleaning the disk. Pi- 
pettes left dirty will be cleaned at the student's expense, or, 
where necessary, a new^one purchased. 



BLOOD 269 

Control Counting. — Count the red corpuscles 
in a second drop. If the result differ greatly 
from that of the first count, the corpuscles in a 
third drop must be counted. 

Counting the White Corpuscles. — Have ready 
a diluting solution of glacial acetic acid (one- 
third of one per cent). This solution will make 
the red cells invisible. Obtain a very large drop 
of blood. By very gentle suction fill the large 
Thoma-Zeiss pipette to the point 0.5. Keep 
the pipette nearly horizontal, both in obtain- 
ing the drop and in drawing in the diluting solu- 
tion ; the bottle should be tilted. Count the 
white corpuscles in the entire ruled disc. Repeat 
with a second drop. Calculate the number of 
white corpuscles in a cubic millimetre. 

Estimation of Haemoglobin 

Oxygen Capacity of the Blood ; the Colorimetric 
Determination of Haemoglobin. 1 — Haldane and 
Smith 2 have shown that " the coloring power of 
the blood of different mammals varies in exact 

1 Haldane : Journal of Physiology, 1901, xxvi, pp. 497- 
504. This experiment should be substituted for that given in 
"Experiments for Students in the Harvard Medical School," 
third edition, pp. 100, 101. 

2 Haldane and Smith : Journal of Physiology, 1900, xxv, 
pp. 331-343. 



270 THE INCOME OF ENERGY 

proportion to its oxygen capacity. The latter 
can be easily and accurately determined by 
means of the ferricyanide method. 1 Thus blood 
of a certain oxygen capacity has also a certain 
coloring power ; and it is possible to standardize 
the coloring power in terms of the oxygen capa- 
city. We can therefore make the unit of volume 
the basis of our definition of the unit of color- 
ing power employed in haemoglobin estimations. 
Since, however, oxy-hsemoglobin is not stable, 
I have adopted as a standard a dilute solution 
of blood of known oxygen capacity saturated 
with coal gas. 2 This solution is sealed up in 
a narrow test-tube after all the contained air 
has been displaced by coal gas, and when thus 
completely sealed is permanent." 

The standard solution for the haemoglobin- 
ometer is a one per cent solution, saturated with 
coal gas, of ox or sheep's blood of the average 
oxygen capacity of the blood of normal adult 
males, found to be 18.5 per cent. If it be borne 
in mind that 100 per cent on the haemoglobin- 
ometer scale corresponds to an oxygen capacity 

1 In this method the oxygen is displaced from laked blood 
by ferricyanide of potassium, and the resultant gas measured. 
Haldane : Journal of Physiology, 1900, xxv, pp. 295-302. 

2 Coal gas contains carbon monoxide as an impurity, and 
thus converts the oxy-haemoglobin to CO-hsemoglobin. 



BLOOD 271 

of 18.5 per cent, it is of course easy to express 
the results in terms of oxygen capacity. The 
exact percentage of haemoglobin corresponding to 
18.5 per cent oxygen capacity is still uncertain. 
According to Hufner's latest results it would be 
13.8 per cent. 

In using the hsemoglobinometer, place 15-20 
c.c. water in the graduated tube, for dilution of 
the blood. Draw 20 cb. mm. of blood into the 
pipette, with the necessary precautions. 1 Gently 
blow the blood out of the pipette on to the sur- 
face of the water in the graduated tube. Before 
mixing the blood with the water introduce into 
the free part of the tube a narrow glass tube con- 
nected with the gas-tap, turn on the gas, and 
push the gas-tube down to near the level of the 
water, so that the air may be instantly displaced 
from the tube. Avoid any loss of liquid. If 
the upper part of the tube, or the liquid itself, 
is warmed by the fingers while the solution is 
being mixed or saturated with carbon monoxide, 
a little liquid is apt to spurt out. This can be 
avoided by holding the tube in a cloth. With- 
draw the gas-tube while the gas is still flowing. 
Close the top of the graduated tube with the 
finger and invert the tube about a dozen times, 

1 See page 264 ; remember not to use blood squeezed from 
the ear. 



272 THE INCOME OF ENERGY 

so that the haemoglobin is thoroughly saturated 
with carbon monoxide and the full pink tint 
of the CO-haeinoglobin appears. Then add water 
drop by drop from a pipette until the tint in 
the graduated tube equals that in the standard 
tube. In comparing the tints of the two tubes, 
it is best to hold them up against the light from 
the sky. The precaution must always be taken 
of repeatedly transposing the tubes from side to 
side during the observations : otherwise very 
considerable error may arise. The percentage 
is read off on the tube after half a minute has 
been allowed for the liquid to run down. An- 
other drop is now added, and if necessary another, 
until the tints again appear unequal. Usually 
the tints will appear equal for two or possibly 
three additions. The mean of the readings which 
gave equality is taken as the correct result. The 
results in successive experiments with the same 
blood should agree within one per cent of the 
mean. 

The average percentage of haemoglobin in the 
blood of women is 11 per cent, and in the blood 
of children 13 per cent below that of adult men. 
In calculating the proportion of haemoglobin in 
the blood of women and children as percentages 
of the average normal proportion, it is evidently 
necessary to add about one-eighth for women 



BLOOD 273 

and one-seventh for children to the percentage 
found by the hsemoglobinometer, with the stand- 
ard solution described above. 

HEMORRHAGE AND REGENERATION 

Determine the specific gravity, number of red 
and white corpuscles per millimetre, and per- 
centage of haemoglobin in the same animal under 
the following conditions : Normal ; two hours 
after a profuse haemorrhage ; one day, three days, 
and five days after the haemorrhage. Plot all 
three curves upon one co-ordinate system. 

Physical Aspects of Coagulation 

Physical Action of Salts in the Coagulation of 
Colloidal Mixtures. — 1. Boil egg-albumin diluted 
with about eight volumes of water. The colloid 
will not coagulate. Add crystals of magnesium 
sulphate gradually. Coagulation will take place. 1 

2. Dip a thin thread of silk in 2 per cent 
solution of calcium chloride and lay the thread 
upon a glass slide beneath a cover-glass. Allow 
boiled solution of egg-white (1 : 8) to run under 
the cover-glass. Examine the process of coagu- 
lation under a magnification of about 500 diam- 

1 Haycraft and Duggan : British Medical Journal, 1890, 
p. 167. 

18 



274 THE INCOME OF ENERGY 

eters. The fluid at first is free from visible 
particles. Near the silk thread appears a fine 
cloud, the particles in which grow in size until 
they form spherules having a maximum diameter 
of 0.75 to 1/x. They are now seen to be arranged 
in patterns forming an open net with regular 
polygonal meshes, having diagonals as long as 6/jl. 
The threads of the net are formed of contiguous 
spherules. This stage, however, is not one of 
equilibrium — the net shrinks, the meshes become 
smaller, and the spherules apparently shift their 
points of attachment until, in place of being 
bounded by threads composed of several spher- 
ules, the image has the appearance of the typical 
fine net with spherules at the nodal points joined 
by tiny threads. Whether these joining-threads 
or bars have a real existence, or whether they 
are purely optical and the spherules actually 
touch one another, it is impossible to say at 
present. When the particles are large enough 
to be clearly visible with a magnification of 500 
diameters they do not show Brownian movement 
— in other words they are probably already in 
some way linked to one another. 

The following explanation of these phenomena 
may be given. On boiling the egg-albumin, the 
heat chemically alters the dissolved proteid and 
produces a suspension of particles having an, 



BLOOD 275 

average diameter commensurable with the mean 
wave-length of light. 1 Under the influence of 
electrolytes (the salt solution) the particles 
aggregate to larger and larger masses. When 
these molecular aggregates attain a certain size 
the fluid condition is no longer possible; this 
would follow immediately from Graham's ob- 
servation that actual coagulation is preceded by 
a continuous increase in the viscosity of the liquid. 
The following conditions determine this generic 
action of salts as coagulants, as distinguished 
from any specific chemical action. 1. The point 
at which coagulation appears is determined by 
the concentration of the solid in the colloidal mix- 
ture, and the temperature, molecular concentra- 
tion (gram-molecules per litre), and nature of 
the electrolytes present. 2. The concentration 
necessary for coagulation is lowered by a rise of 
temperature, or by an electrolyte. 3. The coagu- 
lative energy of electrolytes as measured by the 
number of gram-equivalents per litre necessary 
to produce coagulation is determined almost 
solely by the nature of the metal of the salt ; 
and among the metals themselves it is deter- 
mined by the valency of the metal. 2 

1 Picton and Linder: Transactions of the Chemical 
Society, 1895, lxvii, p. 63. 

2 Hardy: Journal of Physiology, 1899, xxiv, pp. 181-1S3. 



276 THE INCOME OF ENERGY 

Physical Changes in Coagulation. — 1. Clotting 
of Plasma. — Wet a small filter with cane-sugar 
solution (0.5 per cent). Cut a frog's ventricle 
across near the base so that 0.5 c.c. blood shall fall 
into a beaker containing an equal quantity of cane- 
sugar solution. Pour the mixture on the filter. 
Receive the filtrate on a watch-glass. Note- the 
physical changes in this filtrate. 

2. Fibrin Threads. — Place a blood-drop under 
a cover-glass. With the microscope observe the 
appearance of fibrin threads. 

3. Receive 1 c.c. blood into 0.5 c.c. saturated 
solution MgS0 4 . Note (1) absence of clotting, 
and (2) its appearance after dilution. 

4. Receive 0.5 c.c. blood in a watch-glass. 
Let it stand twenty-four hours. Note physical 
changes during the first ten minutes and at 
end of period. 

Secretion 

Speed of Absorption and Secretion. — Place 
5 c.c. of thin starch paste and 2 c.c. concentrated 
nitric acid in each of ten test-tubes and mark 
them 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 
minutes. Let one of each pair of students swal- 
low a gelatine capsule containing ten grains of 
potassium iodide. 1 Immediately rinse the sub- 

1 The subject should have had a small, early breakfast. 



RESPIRATION 277 

ject's mouth until the wash water gives no blue 
color (iodide of starch) on the addition of potas- 
sium iodide and concentrated nitric acid (to set 
free the iodine). Let the subject chew a small 
piece of clean black rubber-tubing to increase 
the secretion of saliva. At intervals of two 
minutes, beginning with the swallowing of the 
potassium iodide, empty the mouth into the cor- 
responding test-tube, at once rinse the mouth 
with water, and begin a fresh collection. 1 

Note the moment at which the drug appears 
in the saliva. 

RESPIRATION 
Chemistry of Respiration 

Estimation of Oxygen, Carbon Dioxide, and 
Water. 2 — Weigh bottles 3, 4, and 5 (4 and 5 

1 If the saliva secreted during two minutes cannot be held 
in the mouth with comfort and without loss by swallowing, the 
mouth may be emptied into a freshly washed porcelain dish, 
from which the saliva should be poured into the proper test- 
tube at the end of each two-minute period. 

2 Apparatus. — Two aspirator bottles, with box. A wooden 
tray, containing a jar for the guinea-pig, and six bottles, viz. : 
Nos. 1 and 4, filled with soda-lime, to absorb carbonic acid ; 
Nos. 2, 3, and 5, filled with pumice stone soaked in sulphuric 
acid, to absorb moisture ; No. 6, a Miiller valve, to prevent air 
being forced back through the series of bottles by a wrong 
coupling of the aspirator tubes. 



278 THE INCOME OF ENERGY 

together). Place the guinea-pig in the jar and 
weigh. During one hour draw air through bot- 
tles 1 to 6 by placing an aspirator bottle on its 
box and allowing the water to flow from this 
bottle to the one remaining on the desk. The 
rubber connecting tube must be changed when 
the aspirator bottles are changed. After one 
hour weigh bottle 3, and bottles 4 and 5. 
Tabulate results as follows : 

grams 

Weight of jar and guinea-pig at beginning 

end . . 



Loss 

Wt. of bottle 3 (sulph. acid) at beginning 

" " end . . 

Gain (= water absorbed) . . . 

Weight of bottles 4 and 5 at beginning . 

end . . . 
Gain (= carbon dioxide absorbed) 

Total water and carbon dioxide absorbed 
Loss in weight of jar and guinea-pig . . 
Difference (= oxygen absorbed) . 
Eespiratory quotient 



Metabolism 

Effect of Muscular Exercise on the Oxygen, Car- 
bon Dioxide, and Water of the Respired Air. — 

Eepeat the estimation of oxygen, carbon dioxide, 



EESP1RATI0N 279 

and water in the respired air (p. 277), slowly 
turning the guinea-pig jar from side to side, so 
that the animal shall be kept in gentle motion 
during an hour. 

The excretion of carbon dioxide is increased by 
muscular exercise. 

Individual Level of Proteid Metabolism. — Each 
group of eight students will select two subjects 
for experiment. They should be thin men in 
good health. Let each subject collect the twenty- 
four hours' urine in a thoroughly clean bottle of 
about 2000 c.c. capacity. Measure the quan- 
tity. Determine in a measured portion of the 
total mixed urine the quantity of urea (hypobro- 
bromite method). Calculate the nitrogen in the 
urea. Add 2.5 grams for the nitrogen excreted 
in the faeces, sweat, and as uric acid in the 
urine. 

Eepeat these determinations for three days, the 
subject maintaining his usual diet and mode of 
life. 

The excretion of nitrogen will probably be 
found to be fairly uniform in each individual 
though the different nutritive habits of different 
individuals may cause them to be on different 
proteid planes, characterized by high, medium, or 
low nitrogen excretion. 

Nitrogenous Equilibrium. — When the daily 



280 THE INCOME OF ENERGY 

excretion of nitrogen has been found to be fairly 
uniform, place the subject upon a simple diet 
of eggs, bread, milk, and butter, containing as 
much nitrogen as he excretes. 1 

The diet may be chosen from the following 
table. 2 

The relative proportion of proteid, fat, and car- 
bohydrate per day should be about as follows : 

Proteid 100 grams 

Fat 100 grams 

Carbohydrate . . . 250 grams 

450 grams 

Eepeat the determination of urea in the urine 
during four more days. 3 Calculate the nitrogen 

1 Owing to the variation in the nitrogen content of meats, 
they should be omitted. 

Physiological heat values : — - 

1 gram proteid = 4000 small calories 

1 " fat =9423 " 

1 " carbohydrate = 4182 " " 

Proteids contain about 16 per cent nitrogen. Hence to obtain 
the amount of metabolized proteid from the nitrogen in the 
urine multiply the latter by 6.25. 

In one pound there are 453.6 grams. 

2 Coffee and tea contain so little nitrogen that they may be 
added to the diet in small amounts to suit the individual taste. 

3 The twenty-four hours should begin in the morning im- 
mediately after passing the urine excreted during the night. 



RESPIRATION 



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282 THE INCOME OF ENERGY 

excreted in urea, adding 2.5 grams for the nitro- 
gen of the faeces, sweat, uric acid, etc. 

It will probably be found that the nitrogen 
excreted equals that ingested (nitrogenous equi- 
librium). 

Effect of Muscular Exercise on Proteid Metab- 
olism. — On the third day of the preceding ex- 
periment, the subject should take an unusual 
amount of measurable exercise. Hill-climbing 
is a suitable form. The protocol of the experi- 
ment must contain an approximate estimate of 
the work done in foot pounds. 

It will be found that muscular work, unless 
pushed to great fatigue, does not increase pro- 
teid metabolism, as measured by the nitrogen 
excreted. 



PART III 
THE OUTGO OF ENERGY 



PART III 
THE OUTGO OF ENERGY 

I Animal Heat 

Regional Temperature. — Kecord the tempera- 
ture taken with a clinical thermometer placed 
under the tongue, in the axilla, and in the 
rectum. 

Effect of Hot and Cold Drinks on the Tempera- 
ture of the Mouth. — Record the temperature 
taken under the tongue soon after drinking (1) 
cold water, (2) warm water. 

Hourly Variation. — Record the temperature 
taken under the tongue every two hours through 
the day and plot the results on clinical tempera- 
ture paper. 

Reaction of Cold and Warm Blooded Animals to 
Changes in the External Temperature. — 1. Record 
the temperature in the gullet of a frog placed in 
water of varying temperature. 2. Record the 
(rectal) temperature of a guinea pig in a bath at 
40°, gradually cooled to 15° C. 

Chemical Action the Source of Animal Heat. ■ — 
Calculate the heat values observed by Rubner 1 

1 Rubner : Zcitsclirift fur Biologie, 1894, xxx, p. 134. 



286 THE OUTGO OF ENERGY 

in a dog weighing 11.8 kg., receiving 580 gms. 
flesh daily. 1 



Date 
1890- 


Total 
Nitrogen 
excreted. 


Fat 
C 


Calories 

from Proteid ; from Fat. 


Total 

calories, 


ril 11 


18.75 


14.6 






12 


17.39 


18.2 






13 


19.43 


13.7 






14 


18.35 


17.5 






15 


18.57 


17.5 






16 


18.50 


16.8 






17 


18.31 


17.1 







Compare above results with those actually ob- 
tained by Kubner when the dog was placed in 
the calorimeter. 



3ate 

.890. 


Heat given 
to calorimeter. 


Heat lost in 
ventilation. evaporation 
of water. 


Total 
calories 
in 24 hrs. 


il 12 


469.4 


44.8 


165.1 


679.4 


13 


483.0 


56.4 


148.6 


687.9 


14 


455.3 


32.9 


178.0 


666.1 


15 


485.1 


34.4 


179.1 


698.7 


16 


447.9 


34.7 


199.3 


681.8 


17 


465.9 


34.1 


174.2 


674.2 


18 


456.9 


35.1 


187.3 


679.4 



1 1 gm. proteid = 4.1 cal. (Rubner used 4.0 cal.) 
1 " fat = 9.3 " ( " " 9.423 " ) 

To find the fat from the carbon multiply the carbon by 1.3 
(fat contains 76.5 per cent of carbon). 



THE ELECTROMOTIVE PHENOMENA 287 



II 



THE ELECTKOMOTIVE PHENOMENA OF 
MUSCLE AND NERVE 

The stored energy of muscle is set free in molec- 
ular movement, — heat, chemical action, and 
electricity, — and in mechanical work, the change 
in form. It will be convenient to consider the 
electromotive phenomena first. 

The Demarcation Current of Muscle 

Demarcation Current of Muscle. — 1. Mount 
two non-polarizable electrodes. Connect them 
to the capillary electrometer through a short- 
circuiting key. Eemove a sartorius muscle. Cut 
off each end with a sharp knife by a clean cut at 
right angles to the fibres. Observe that the 
muscle is thereby converted into a " muscle 
prism." It possesses two artificial cross-sections, 
at each of which the muscle has been injured, 
and is, in fact, dying, and an uninjured natural 
longitudinal surface. Place the muscle across 
the electrodes so that the cross-section rests on 
one electrode and the middle of the longitudinal 
surface rests on the other. Bring the meniscus 
of the capillary into the field. Note its position 
on the micrometer scale. Open the key. 



288 THE OUTGO OF ENERGY 

The meniscus will be displaced in the direc- 
tion indicating a higher potential at the middle 
or " equator " of the longitudinal surface than 
at the cross-section. .Note the divisions of the 
scale, traversed by the meniscus — the displace- 
ment is proportional to the difference of potential. 

2. Move the electrode on the longitudinal sur- 
face a few millimetres towards the cross-section. 
Determine the difference of potential here. It 
will be less than before. Measure the potential 
in similar manner at intervals of 5 mm. between 
this point and the cross-section. On co-ordinate 
paper set down on the abscissa the number of 
millimetres from equator to cross-section. Set 
down as ordinates the number of divisions of the 
micrometer scale traversed by the meniscus when 
the electrode on the longitudinal surface is placed 
successively on the equator, and at intervals of 5 
mm. between equator and cross-section. Draw 
the curve uniting the summits of the ordinates. 

As the cross-section is approached, the curve of 
potential will fall more and more rapidly. The 
centre of the cross-section is negative towards 
the outer parts of the section. Points on the 
equator, or equidistant from it, have the same 
potential. Points on the longitudinal surface 
at different distances from the equator, and on 
the cross-section at different distances from the 



THE ELECTROMOTIVE PHENOMENA 289 

centre of the section, show a slight difference of 
potential. 

Prove these several statements. 

Ohlique Section. — When the artificial cross- 
section is oblique to the long axis of the muscle, 
the maximum difference of potential is no longer 
at the equator and the centre of the cross-section. 
The most positive point is on the longitudinal 
surface near the obtuse angle made by the oblique 
section, and the most negative point is on the 
cross-section near the acute angle. The structure 
of certain muscles, the frog's gastrocnemius, for 
example, is such as to make their natural cross- 
section oblique. In consequence, their differ- 
ences of potential are not distributed as in a 
regular parallel-fibred muscle like the sartorius. 
In the gastrocnemius, owing to the peculiar inser- 
tion of the muscle fibres into the tendon, the 
upper end of the muscle is really the middle of 
the longitudinal section, while the lower end 
is the acute angle of an oblique cross-section. 
When the ends are connected with an electrom- 
eter, a strong current is observed flowing (out- 
side the muscle) from the upper to the lower end. 

Uninjured Muscle. — Prepare a sartorius muscle 
with extreme care to prevent injury. Connect 
the tendon (the natural "cross-section") and 
the longitudinal surface with the electrometer 

19 



290 THE OUTGO OF ENERGY 

through a short-circuiting key. Note the posi- 
tion of the meniscus on the micrometer scale. 
Open the short-circuiting key. 

The meniscus will move but little. It will not 
move at all, provided the muscle has not been 
injured; but the difficulty of preparation is such 
that some difference of potential will probably 
appear. 

Close the key. Injure the muscle by drawing 
a hot wire across one end. Open the key. 

A strong demarcation current will appear. 

Stimulation by Demarcation Current. — 1. Make 
a nerve-muscle preparation (sciatic nerve and 
gastrocnemius muscle). Let the nerve near the 
muscle touch a cross-section of the sartorius. 
Now let the end of the nerve fall on the longi- 
tudinal surface near the equator. 

The gastrocnemius will contract; the nerve 
acts as a conductor between the positive longi- 
tudinal surface and the negative cross-section. 

It should be pointed out that the conclusion 
here drawn is not entirely free from criticism. 
The muscle is a conductor as well as the nerve, 
and may close the demarcation current of the 
nerve, as the nerve may close that of the muscle. 
Thus it is possible that the nerve is stimulated 
by its own demarcation current. The former 
explanation is the more probable. 



THE ELECTROMOTIVE PHENOMENA 291 

2. Place non-polarizable electrodes on the 
longitudinal surface and cross-section of the 
sartorius. Fasten the wires of the stimulating 
electrodes in the binding posts of the non-polar- 
izable electrodes. Drop the nerve of the nerve- 
muscle preparation across the electrode points. 

The gastrocnemius will contract when the 
nerve bridges the space from one electrode to 
the other, and thus completes the circuit be- 
tween the longitudinal surface and cross-section 
of the sartorius. 

3. Place a little 0.6 per cent solution of sodium 
chloride in a porcelain dish. Fasten one end of 
the sartorius gently between two pieces of cork 
in the jaws of the muscle clamp. Bring the 
muscle over the saline solution. Make a fresh 
clean cross-section, and lower the clamp on its 
stand until the cross-section dips (not too far) 
into the solution. 

The muscle will twitch. The twitch will pull 
the end of the muscle out of the solution. When 
the muscle relaxes, the contact between positive 
longitudinal surface and negative cross-section 
is once more made by the saline solution, the 
current of rest flows from the point of higher to 
'the point of lower potential, and again stimulates 
the muscular tissue through which it passes. 
Thus the muscle is stimulated by its own cur- 



292 THE OUTGO OF ENERGY 

rent. A long series of contractions may be 
secured. Other liquid conductors will serve. 
When the solution touches only the cross-sec- 
tion, there is no contraction. 

4. Prepare a fresh sartorius muscle with bony 
attachments. Fasten the pelvic end in the 
muscle clamp. Make a fresh cross-section in 
the first sartorius. Hold the tibial end of the 
second muscle in such a way that the muscle 
lies horizontally with its upper surface some- 
what concave. Against this surface bring the 
fresh cross-section of the first sartorius. The 
longitudinal surface will naturally also touch 
to some extent. 

The second muscle will close the circuit be- 
tween longitudinal surface and cross-section of 
the first, and, if very irritable, both muscles will 
contract. 

Interference between the Demarcation Current 
and a Stimulating Current ; Polar Refusal. — Con- 
nect a dry cell through an open key with the 
and 1 metre posts of the rheochord (Fig. 46). 
Mount two non-polarizable electrodes, and con- 
nect them through a pole-changer (with cross- 
wires) to the positive post and slider of the 
rheochord. Tie a thick cotton thread to the 
foot of the positive electrode in such a way 
that the thread shall hang down in a small loop. 



THE ELECTROMOTIVE PHENOMENA 293 

Let a sartorius muscle rest on a clean glass 
plate. Make an artificial cross-section by draw- 
ing a hot wire across the muscle near the pelvic 
end. Pass the loop of thread on the positive 
electrode over the muscle about 5 mm. from the 
thermal cross-section. Let the negative electrode 
rest on the cross-section. Arrange the rheochord 
for weak currents. Moisten the electrodes with 
normal saline solution. Close the key. 

The usual closing contraction 
will be absent (polar refusal). 

Note that the galvanic cur- 
rent is now passing through 
the muscle in an atterminal 
direction, i. e. towards the in- 
jured portion (admortal), while 
the demarcation current is 
passing through the muscle in Fl 'g- ^- 

the opposite direction. The two currents more 
or less compensate each other. Hence, the ab- 
sence of the closing contraction. Observe, also, 
that opening the key will break the galvanic cir- 
cuit, but that the circuit for the demarcation 
current will still be closed — through non-polariz- 
able electrodes and rheochord. 

Open the key. 

An opening contraction will take place, 
obviously because the muscle current is no 
longer compensated. 




294 THE OUTGO OF ENERGY 

Eeverse the pole-changer, so that the anode 
lies at the cross-section. Open and close the 
galvanic current. 

Contraction will take place at closure only. 
The electrode at the cross-section again refuses. 

2. Compensation Method. — The electromotive 
force of a current of injury may be expressed in 
fractions of a Daniell cell, or any other constant 
element, by bringing into the same circuit with the 
current of injury, but in an 
opposite direction, so much 
of the current from the cell 
as will exactly balance the 
current of injury, i. e. so 
much as will keep the menis- 
cus of the electrometer from 
moving in either a positive 
or negative direction when 
Fi s- 47 - connected with the circuit. 

Prepare a sartorius muscle. Connect a Daniell 
cell with the and 10 metre posts of the rheo- 
chord. Connect the capillary electrometer to a 
closed short-circuiting key. From the post joined 
to the capillary lead to the post of the rheo- 
chord. Connect the remaining post of the key 
to a non-polarizable electrode placed on the cross- 
section of the muscle. Join the slider of the 
rheochord to another non-polarizable electrode 




THE ELECTROMOTIVE PHENOMENA 295 

placed on the equator of the muscle (Fig. 47). 
Bring the slider to the zero post. Bring the 
meniscus into the field. Note its position on the 
micrometer scale. Open the short-circuiting key. 
When the meniscus comes to rest, move the slider 
along the rheochord until the meniscus returns 
to its original position. Bead the number of. 
millimetres between the positive post and the 
slider. This number divided by 10,000 is the 
fraction of the electromotive force of the Daniell 
cell (1.1 volt) necessary to balance the current of 
injury of the muscle (from 0.035 to 0.090 volt). 

Demarcation Current of Nerve 

Place non-polarizable electrodes on the cross- 
section and longitudinal surface of a long piece 
of sciatic nerve. Connect the electrodes through 
a short-circuiting key with the electrometer. 
Bring the meniscus into the field and open the 
short-circuiting key. 

The meniscus will move in a direction indicating 
a current in the nerve from cross-section to longi- 
tudinal surface, as in muscle. 

Measure the electromotive force of this demar- 
cation current. 

The demarcation current is much weaker in 
nerve than in muscle, being in the former about 



296 THE OUTGO OF ENERGY 

0.025 volt, as against about 0.060 volt in 
muscle. The demarcation current of muscle is 
maintained in force for a long time, whereas that 
of nerve diminishes rapidly. The nerve current 
is restored on making a fresh cross-section. 

The demarcation current from the cut branches 
of a nerve may reach electrodes placed on the 
main trunk, and thus confuse the electrometer 
measurements. To this same cause must be 
ascribed the increased irritability observed in the 
main trunk in the neighborhood of branches ; 
the irritability is raised by the demarcation cur- 
rent of the severed branch. 

Nerve may be stimulated by its own Demarca- 
tion Current. — On a glass plate make a U shaped 
wall of normal saline clay, each limb about 1 cm. 
long and 3 or 4 mm. wide. Carefully remove the 
moisture between the clay walls with filter paper. 
Lay the longitudinal surface of the nerve of a nerve- 
muscle preparation on one limb of the U, and with a 
glass rod let the cross-section fall on the other limb. 

When the circuit between the cross-section and 
the longitudinal surface is completed by contact 
with the clay, the demarcation current will 
stimulate the nerve, and the resulting nerve im- 
pulse will cause the muscle to contract. 

Other Examples. — The dropping of the central 
end of the severed vagus nerve into the wound 
from which it was lifted has caused the slowing 



THE ELECTROMOTIVE PHENOMENA 297 

of respiration, presumably by the stimulation of 
the nerve through the closure of its own demar- 
cation current by the lymph or blood, though 
the possible influence of demarcation currents 
from the wounded tissues cannot be forgotten. 
Definite results, such as inhibition of the heart, 
have not been observed to follow the closure of 
the current of the peripheral segment. To avoid 
any chance stimulation from the closure of the de 
marcation current, nerves are sometimes severed 
physiologically by freezing, — a process which 
not only does not stimulate, but which does not 
destroy permanently the conductivity ; the latter 
returns upon the restoration of the nerve to 
normal temperature. 

The olfactory nerve of the pike shows a strong 
demarcation current, as does the optic nerve. 



Hypotheses regarding the Causation of 
the Demarcation Current 

Make artificial cross-sections in a sartorius 
muscle, and test the difference of potential be- 
tween the longitudinal surface and a cross-section 
with the electrometer. Divide the muscle, longi- 
tudinally, and make fresh cross-sections ; test the 
difference of potential again. 

However small the muscle prism may be 



298 



THE OUTGO OF ENERGY 



made, the longitudinal surface will still be posi- 
tive to the cross-section. 

Molecular Hypothesis. — The fact that the 
smallest possible muscle prism is still positive 
on the longitudinal surface, and negative on the 
cross-section, suggested to DuBois-Keymond that 
muscle (and nerve) are composed of electrical 
particles or molecules something like the mole- 
cules of a magnet. A magnet has two poles, 
and, however it may be divided, the pieces still 



hhuihhThhwhhi i 

■lllllllllllllllll J 

■IIIIIIIIIIHIIIIIII 



Fig. 48. Scheme of the myomeres in a parallel-fibred muscle (Rosenthal). 



possess a north and a south pole. The magnet is 
therefore believed to be composed of molecules, 
each possessing a north and a south pole. These 
molecules lie with the north poles all pointing in 
one direction, the south poles in the other. The 
structure of muscle favors, in a measure, a simi- 
lar hypothesis ; for it is known that a striated 
muscle consists of fibrillse, each of which is com- 
posed of a row of particles arranged in quite 
regular fashion. The electromotive molecules, or 



THE ELECTROMOTIVE PHENOMENA 



299 



myomeres, may be conceived to be positive on 
their longitudinal surfaces, and negative on their 
cross-sections (Fig. 48). They are assumed to 
have their negative surfaces turned towards the 
ends of the muscle or nerve, and the positive 
equatorial region turned towards the longitudi- 
nal surface. A non-electric conducting substance 
surrounds them. An electrode placed on the 
longitudinal surface would touch only the posi- 
tive sides, while an electrode placed on the cross- 




HIHMk 

flHI 
■MM 
■l—l 



Fig. 49. Scheme of myomeres in an oblique section (Rosenthal). 



section would touch only the negative poles. 
However small the muscle prism was made, the 
relation would still be the same. Thus the dis- 
tribution of potentials would correspond with 
that actually observed. 

When the cross-section is oblique, the myo- 
meres at the cross-section are exposed as shown 
in Fig. 49, and the currents which pass from the 
longitudinal surface of each myomere to its cross- 
section are added to the main currents passing 



300 THE OUTGO OF ENERGY 

from the longitudinal surface to the cross-section 
of the whole muscle. The region of maximum 
positive potential is thereby brought towards the 
obtuse angle of the oblique cross-section, and the 
region of maximum negative potential is dis- 
placed towards the acute angle, as actually 
observed. 

When it was found by Bernstein, Hermann, 
and others, that uninjured muscle showed no 
difference of potential, DuBois-Beymond as- 
sumed that in the natural, uninjured state the 
end of the muscle in contact with the tendon 
(the " natural cross-section ") is composed of a 
layer of molecules which have their positive in- 
stead of negative surface turned towards the 
tendon. 

The highly artificial and complicated structure 
which DuBois was compelled to erect on this 
foundation in order to explain all the electrical 
phenomena of living tissue, cannot be discussed 
here. The chief argument against the molecular 
theory of muscle and nerve currents is that the 
phenomena can be explained in a simpler way. 

Alteration Theory. — This hypothesis, in the 
making of which Hermann and Hering have 
been especially active, explains the electromo- 
tive forces of nerve and muscle by alterations in 
the chemical composition of the tissue at the 



THE ELECTROMOTIVE PHENOMENA 301 

cross-section. When the cross-section is made, 
the tissue next the section passes through the 
series of catabolic changes which constitute 
muscle death ; carbon dioxide is given off, lac- 
tic acid is developed, a soluble proteid is con- 
verted to a less soluble form, etc. The contact 
of this dying layer with the uninjured tissue is 
believed to create a difference of potential. The 
potential difference, therefore, appears at the de- 
marcation between dying and uninjured tissue, 
— hence the term "demarcation current." The 
action current finds its explanation in the chemi- 
cal changes accompanying contraction. It would 
be interesting to consider here the parallel be- 
tween the chemical transformations in contrac- 
tion and those which usher in the death of the 
muscle, but we must be content with mentioning 
the apparently close relationship. In its most 
general form, the alteration hypothesis rests on 
the fact that living substance is everywhere the 
seat of constant constructive and destructive 
changes. Where these are nearly in equilibrium, 
as, for example, in the resting uninjured muscle, 
the tissue is equipotential ; where, on the con- 
trary, either form of chemical change has the 
upper hand, as in the explosion which we term 
contraction, and in dying muscle, it is assumed 
that a difference of potential is created. 



302 THE OUTGO OF ENERGY 

For many years the weight of physiological 
opinion has been largely on the side of the alter- 
ation hypothesis ; but it would be unsafe without 
further evidence to decide finally against the 
molecular theory. 

Action Current of Muscle 

The demarcation current (current of injury, 
current of rest) just studied has been shown to 
be due to the injury of the tissue. We have 
now to examine the electromotive forces which 
appear when a nerve or muscle becomes active. 

1. Rheoscopic Frog. — Make two nerve-muscle 
preparations, A and B. Let the nerve of B 
rest on muscle A. Stimulate the nerve of A 
with single induction shocks, and with the 
tetanizing current. 

Muscle B will contract once for each contrac- 
tion of A. The current of action of muscle A 
stimulates the nerve of B. 

Secondary contraction can take place also from 
muscle to muscle, but only under circumstances 
that suggest increased irritability, as, for example, 
through partial drying. No secondary contrac- 
tion has been secured from voluntary muscular 
contraction. 

2. That the stimulus to the nerve of the rheo- 
scopic muscle is really an electrical current, is 



THE ELECTROMOTIVE PHENOMENA 



303 



shown by the capillary electrometer. Place 
muscle A in the moist chamber upon two non- 
polarizable electrodes. Let the tendon rest on 
one electrode and the equator on the other. Lead 




\Zs 



Fig. 50. The vibrating interrupter. A platinum wire on the end of a steel 
spring dips into a mercury cup. By varying the length of the spring, con- 
tacts from once a second to more than one hundred per second may be 
secured. 

from the non-polarizable electrodes through a 
closed short-circuiting key to the capillary elec- 
trometer (the tendon should be connected with 



304 



THE OUTGO OF ENERGY 



the capillary). Lay the nerve on stimulating 
electrodes. Connect the latter with the secondary 
coil of an inductorium arranged for single induc- 




ing. 51. The vibrating interrupter arranged to make one contact per 
second. 



tion currents. Place the vibrating interrupter 
(Figs. 50, 51) in the primary circuit. Bring the 
meniscus into the field. Open the short-circuiting 



THE ELECTROMOTIVE PHENOMENA. 305 

key. The meniscus will be displaced by the 
demarcation current. When the meniscus has 
come to rest, stimulate the nerve with single and 
repeated induction currents. 

With each stimulus there will be a negative va- 
riation (action current) of the demarcation current. 

When the number of stimuli per second passes 
a certain point, which differs with different in- 
dividuals, the hitherto separate excursions of the 
meniscus will be fused, and a gray blur will 
appear at the end of the vibrating column. 
Movements of this rapidity may of course be 
studied by photographing them on sensitive paper 
moving rapidly enough to draw the fused image 
out into a line in which its component oscilla- 
tions are each distinct, or they may be observed 
directly by the stroboscopic method. 

The Action Current in Tetanus ; Stroboscopic 
Method. — 1. If a piece of thin black paper about 
1 cm. square is fastened vertically on the end of 
the electro-magnetic signal lever, and the signal 
placed in the primary circuit of the inductorium 
arranged for tetanizing currents, the piece of 
paper will move each time the primary current 
is made or broken by the vibrating hammer of 
the inductorium. The movement is so rapid 
that the paper seems stationary and a gray haze 
appears on its upper and lower border. 

20 



306 THE OUTGO OF ENERGY 

Connect the electrometer with the secondary 
coil of the inductorium, and bring the vibrating 
meniscus into the field. 

Bring the stroboscopic paper next the acid 
reservoir of the electrometer at such a height 
that the edge of the meniscus shall be seen 
through the gray blur. The meniscus will no 
longer appear blurred, but will be as sharp as 
if the mercury were stationary. This appearance 
is produced only when the stroboscopic paper 
and the object seen by its aid have the same 
periodicity of vibration. If the periodicity of 
the vibrations is unequal, interference results, 
and from this interference the rate of vibration 
of the observed body can be calculated. For 
example, if the observed body shows three vibra- 
tions per second, when observed through the 
stroboscope, its rate is three more per second 
than that of the stroboscope. 

In the present instance, the meniscus remains 
apparently at rest. The number of action cur- 
rents is therefore identical with the number of 
stimuli. 

2. Rheoscopic Muscle Tetanus. — The same 
method may be applied to the analysis of the 
rheoscopic tetanus in the rheoscopic muscle. 

Place two nerve-muscle preparations in the 
moist chamber. Place the tendon of muscle B 



THE ELECTROMOTIVE PHENOMENA 307 

on one electrode and the longitudinal surface on 
the other, and connect them through a short- 
circuiting key with the electrometer. Lay the 
nerve of B on muscle A. Place the nerve of A 
on electrodes connected with the secondary coil 
(the coil should be well over the primary). 
Bring the meniscus into the field, and open the 
short-circuiting key. Place the stroboscope, still 
in the primary circuit, near the meniscus. Tet- 
anize the nerve of A. 




Fig. 52. 

For each stimulus received from nerve A, 
muscle A contracts ; the contractions are so fre- 
quent that they fuse into tetanus. At each 
contraction of A, its current of action stimulates 
the nerve of B, and B also contracts. At each 
contraction of B, the action current displaces 
the meniscus, which falls therefore into very 
rapid oscillation. Observe the meniscus through 
the stroboscope. It will seem to be standing 
still. 



308 THE OUTGO OF ENERGY 

Thus the apparent continuous contraction of 
muscle B is in reality a series of simple contrac- 
tions, as stated, corresponding in number to 
the make and break currents of the inductorium. 
For each contraction there is one action current 
in each muscle. 1 

When a muscle and its nerve are removed 
without injury to the muscle, electrodes placed 
on the latter will show no difference of potential, 
as already stated (page 289). Stimulation of such 
a muscle through its nerve causes a current of 
action to start at the point at which the nerve 
enters the muscle fibres. The contraction wave 
begins also at this point, as may be shown very 
beautifully by "fixing " the contraction in the 
muscles of certain insects by plunging the con- 
tracting muscle into a solution which arrests and 
" sets " the fibre instantly. In such cases fibres 
will be found in which the contraction wave is 
caught at its beginning in the neighborhood of 
the nerve end-plate. 

The action current, beginning at the entrance 
of the nerve into the muscle fibre, passes in both 
directions along the fibre. As may be shown 
with the differential rheotome, or by photograph- 
ing the meniscus of the capillary electrometer, 

1 The experiment also demonstrates that the meniscus has no 
after vibrations, but follows unerringly the changes of potential. 



THE ELECTROMOTIVE ^PHENOMENA 309 

the current is diphasic. In the first phase, the 
current is directed away from the nerve, in 
the second phase, towards it. In extirpated 
muscle, the second phase is much weaker than 
the first. In normal muscle in situ (human 
muscle), this difference or decrement does not 
appear. 

The direction of the current obtained with 
the electrometer from the ivliole muscle is de- 
termined by the position of the electrodes with 
reference to the nerve equator, namely, a trans- 
verse line drawn at the mean distance from the 
entrance of all the nerve fibres. Points nearer 
the equator are negative to points further away. 

Action Current of Human Muscle. — Cover 
the brass electrodes with cotton saturated with 
saline solution, and connect them with an 
inductorium arranged for tetanizing currents. 
Close the short-circuiting key of the second- 
ary coil. Tie about each of the non-polarizable 
electrodes a piece of well washed candle-wick a 
foot long. Saturate the wick with sodium 
chloride solution. Place one of these elec- 
trodes around the forearm near the elbow, the 
other around the wrist. (The nerve equator lies 
about the upper third of the forearm.) Connect 
the electrodes through a short-circuiting key 
with the capillary electrometer. Place the brass 



310 THE OUTGO OF ENERGY 

electrodes over the brachial plexus in the axilla. 
Bring the meniscus into the field. Open the 
short-circuiting key leading to the electrometer. 
If the meniscus is displaced by a skin (secretion) 
current bring it back by means of the pressure 
apparatus. Set the inductorium in action. Open 
the short-circuiting key of the secondary coil, 
thus stimulating the nerves. 

The meniscus will be displaced by an action 
current. 

Action Current of Heart. — 1. Expose the 
heart of a frog (page 112). Lay the nerve of an 
irritable nerve-muscle preparation on the beating 
ventricle. 

During diastole, the rheoscopic muscle will be 
quiet ; at each systole, it will contract. 

2. Tie a cotton thread one inch long about the 
foot of each non-polarizable electrode, and let 
the ends, wet with normal saline solution, rest 
on the beating heart, one on the base, the other 
on the apex. These electrodes will follow the 
movements of the heart. Connect the elec- 
trodes through a short-circuiting key to the 
electrometer. 

During the diastole, the meniscus will remain 
at rest. At each beat of the ventricle, the 
meniscus will move ; first in a direction indicating 
that the base is negative to the apex, and then 



THE ELECTROMOTIVE, PHENOMENA 311 

in the opposite direction. The action current 
passes over the heart from base to apex. 

These experiments show not only that there 
is an action current at each systole of the heart, 
but are evidence also that the resting heart 
muscle is iso-electric (i. e. of uniform potential). 

The Action Current precedes the Contraction. — 
Expose the heart. Fasten a very fine copper wire 
to the ventricle ; the end of the wire may be 
thrust through the tip of the ventricle. Mount 




Fig. 53. The Heart Lever. 

the heart lever (Fig. 53) on a stand so that the 
writing point will write on the smoked paper of 
the kymograph. Bring the free end of the wire 
to the heart lever, on which it may be fastened 
with a drop of colophonium cement. Make a 
nerve-muscle preparation. Fasten the femur in 
the upper side of the muscle clamp, at right 
angles to the long axis of the clamp. Bring the 
latter near the heart lever, so that the nerve may 
rest on the ventricle. Fasten the tendon Achilles 
to the muscle lever by a thread which passes over 
the pulley on the axis of the lever before being 



312 THE OUTGO OF ENERGY 

secured to the lever. Thus the muscle, though 
below the lever, will pull it upwards wheu con- 
traction takes place. Let the two writing points 
be in the same vertical line. Start the drum at 
rapid speed. Two curves will be recorded : one 
by the contraction of the ventricle, the other by 
the rheoscopic muscle, stimulated to contract by 
the action current. The contraction of the rheo- 
scopic muscle will slightly precede the contraction 
of the ventricle. 

Current of Action of Human Heart. — Place 
normal saline solution in two beakers. In each 
let the foot of a non-polarizable electrode dip. 
Connect the electrodes throuqh the usual short- 
circuiting key with the electrometer. Bring the 
meniscus into the field. Let an assistant place a 
finger of each hand in the saline solution. 

When the short-circuiting key is opened the 
meniscus will be displaced by the skin (secretion) 
current. Careful observation will show also a 
periodic variation synchronous with the systole 
of the heart. 

The diphasic character of the action current of 
the heart, shown so well by the capillary elec- 
trometer to the unaided eye, appears even more 
clearly when the movements of the meniscus are 
recorded by projecting them on a quickly moving 
photographic plate. By photography, too, the di- 



THE ELECTROMOTIVE PHENOMENA 



313 



phasic character of the action current in the more 
rapidly contracting skeletal muscle is made visible, 
and the form of the action current wave recorded. 
Before the capillary electrometer was used for 




Fig. 54. Scheme of differential rheotome. 



this purpose, the differential rheotome of Bern- 
stein was employed. This celebrated invention 
consists of a wheel which revolves at uniform 
speed and carries contacts by which the primary 
circuit of an inductorium and a galvanometer 



314 THE OUTGO OF ENERGY 

circuit may be made. By means of the induc- 
torium, the muscle is stimulated at one end. 
The galvanometer records the current of action 
by means of electrodes placed at the other end 
of the muscle. The position of the galvanometer 
contact on the wheel can be shifted nearer to or 
farther from the stimulating contacts ; thus the 
interval between stimulation and the making of 
the galvanometer circuit may be chosen at will, 
and the electromotive force at any point in the 
action wave registered. By repeatedly changing 
the interval, the several portions of the wave 
can be investigated successively, and the results 
plotted. With Hermann's rheotachygraph, the 
whole electrical change may be recorded at one 
time. In this instrument the stimulating con- 
tacts revolve rapidly, and the galvanometer con- 
tact less rapidly, so that the interval between 
stimulation and the closure of the galvanometer 
continually alters. The effect of the electrical 
change on the galvanometer is thus prolonged so 
that the galvanometer mirror is able to follow it. 
The results from these different methods agree 
in showing that the electrical change sweeps 
over the muscle (and nerve), in the form of a 
wave at a rate, in frog's muscle, of about three 
metres per second. The duration of the wave 
is from 0.0033 to 0.0040 second. The ascent is 



THE ELECTROMOTIVE PHENOMENA 315 

quicker than the descent. The latent period is 
probably absent ; the process begins as soon as 
the stimulus reaches the muscle. The electro- 
motive force of the action current for a single 
contraction of the frog's gastrocnemius is about 
0.08 volt. 

Direct stimulation of the whole of a normal 
uninjured muscle produces no action current 
whatever, because the whole muscle becomes 
active at the same moment. 

Action Current of Nerve 

1. Negative Variation. — Sever the nerve of a 
nerve-muscle preparation close to the muscle, 
and lay the nerve in the moist chamber on non- 
polarizable electrodes placing the equator on one 
and a cross-section on the other. Lead them 
through a short-circuiting key to the capillary 
electrometer. Place a second pair of non-polar- 
izable electrodes near the other cross-section 
of the nerve. Connect this second pair to the 
secondary coil of an inductorium. Connect the 
primary coil through a key and the wheel inter- 
rupter with a dry cell. Bring the meniscus into 
the field. Open the short-circuiting key. The 
meniscus will be displaced by the demarcation 
current. Stimulate the nerve with induction 
shocks at different rates. 



316 THE OUTGO OF ENERGY 

A negative variation will be observed each 
time the nerve is stimulated. 

2. The current of action is not dependent on 
the electrical stimulation, but is an expression of 
the changes in the nerve which constitute the 
nerve impulse. It follows mechanical as readily 
as electrical stimulation. 

Lead to the capillary electrometer from non- 
polarizable electrodes placed on the longitudinal 
surface and cross-section. Note the position of 
the meniscus. Stimulate the nerve mechanically 
by snipping the end with the scissors. 

There will be a negative variation as before. 

Positive Variation. — The direction of the cur- 
rent of action is not always opposite to that of 
the demarcation current. Biedermann obtained 
a current in the positive direction on stimulating 
the nerve to the abductor muscle in the lobster. 
In the tortoise, the cardiac auricle may be cut 
away from the sinus, without injury to the cor- 
onary nerve, which in this animal carries to the 
auricle the cardiac fibres of the vagus. After 
this operation, the auricle and ventricle remain 
motionless for a time. In a heart thus prepared, 
Gaskell made a thermal cross-section by im- 
mersing the tip of the auricle in hot water, and 
led the demarcation current to a galvanometer. 
The stimulation of the vagus in the neck — the 



THE ELECTROMOTIVE PHENOMENA 317 

heart still resting — ■ caused a marked increase in 
the demarcation current, in other words, a posi- 
tive variation. No visible change in the form of 
the heart was observed. 

Positive After Current. — Compensate the de- 
marcation current of nerve by the method de- 
scribed on page 294. When compensation is 
secured, note the position of the meniscus on the 
scale, and tetanize the nerve. The meniscus will 
be displaced by the current of action. Note the 
direction of the current. Break the stimulating 
current. The meniscus will return to and pass 
the position which it held when the demarca- 
tion current was compensated, showing thus a 
current opposed in direction to the action 
current. 

The positive after current is absent in weak- 
ened or fatigued nerves. 

Contraction secured with a Weaker Stimulus 
than Negative Variation. — Place the non-polariz- 
able electrodes on the longitudinal surface of the 
nerve of a nerve-muscle preparation. Connect 
them through the usual short-circuiting key 
with the electrometer. Bring the meniscus into 
the field. Arrange the inductorium for break 
currents. Place the secondary coil some dis- 
tance from the primary. Stimulate the nerve 
in the extrapolar region. Approach the coils 



318 THE OUTGO OF ENERGY 

until the threshold value is reached and the 
muscle contracts. 

At the threshold value of muscular contrac- 
tion, the current of action in the nerve will not 
yet be demonstrable. The coils must be still 
nearer together before the action current be- 
comes visible. 

This experiment has a certain suggestive 
value. It would not, however, be safe to con- 
clude from it that the action current is not 
an essential part in the passage from the resting 
to the active stage. The failure to recognize the 
action current probably lies in the method. 

Current of Action in Optic Nerve. — Place two 
non-polarizable electrodes in the moist chamber, 
and connect them through a short-circuiting key 
with the capillary electrometer. Remove the 
eye of the frog, together with a portion of the 
optic nerve, and lay the preparation on the elec- 
trodes in the moist chamber, letting the edge of 
the cornea touch one electrode and the optic 
nerve the other. Cover the electrodes and the 
preparation with a black pasteboard box or 
other opaque screen to shut off the light. Xote 
the position of the meniscus in the field of 
the microscope. Open the short-circuiting key. 
A demarcation current from the injured optic 
nerve to the cornea will be indicated. Re- 



THE ELECTROMOTIVE PHENOMENA 319 

move the box so that light shall fall on the 
retina. 

The demarcation current will undergo a nega- 
tive variation. 

Shut off the light by replacing the box. 

There will now be a positive variation. 

Currents of action have also been demonstrated 
in the central nervous system. Gotch and 
Horsley find that when the spinal cord of the 
monkey is severed, and non-polarizable electrodes 
are applied to the longitudinal surface and the 
cross-section, a negative variation of the current 
of injury appears whenever the cortex of the 
cerebrum is stimulated in the neighborhood of 
the fissure of Kolando, — the " motor " region. A 
considerable degree of localization in the cord is 
possible. It may be shown that the negative 
variation from the motor region of the cortex 
descends the cord chiefly in the crossed pyramidal 
tract, — a collection of white fibres in the lateral 
column of the cord near the gray matter. It is 
known from pathological evidence that the nerve 
impulse from the motor cortical cells passes 
through these fibres, and the demonstration of 
their negative variation justifies the hope that 
this method may be useful in determining the 
course of other nerve fibres in the brain and 
cord. 



320 THE OUTGO OF ENERGY 

Errors from Unipolar Stimulation. — Attention 
already has been called to the danger of unipolar 
induction currents entering the electrometer 
circuit in observations of the action current with 
the capillary electrometer or galvanometer (page 
74). 

Place a nerve in the moist chamber. Connect 
the capillary electrometer through a short-circuit- 
ing key with non-polarizable electrodes placed on 
the longitudinal surface and cross-section, about 
5 mm. apart. Let a wire connected with one 
pole of the secondary coil rest on the nerve about 
2 cm. from the non-polarizable electrodes. Open 
the short-circuiting key. When the meniscus 
has come to rest, set the inductorium in action. 

If the meniscus remains at rest, bring the 
secondary coil nearer the primary, until unipolar 
effects appear. 

Secretion Current 

Secretion Current from Mucous Membrane. — 

Eemove the skin from the lower jaw of a frog, the 
skull of which has been cut away. Be very care- 
ful not to touch the tongue with metal instruments 
or with fragments of skin. Make a normal saline 
clay electrode about 1 cm. square and 3 mm. 
thick on the glass of the cork clamp near the 



THE ELECTROMOTIVE PHENOMENA 32l 

cork. Lay the denuded jaw on the glass, and 
turn the tongue forward with a glass rod until 
the tip can be secured in the clamp. Avoid all 
roughness. The normally upper surface of the 
tongue will now rest on the clay. Bring one 
non-polarizable electrode into contact with the 
clay, and let the other touch the upper (normally 
low^er) surface of the tongue. Connect the elec- 
trodes through an open key with the capillary 
electrometer. Bring the meniscus into the field, 
and note its position on the micrometer scale. 
Close the key. 

A strong difference of potential will be shown. 
The normal under surface is usually positive 
towards the normal upper surface. 

The difference of potential thus demonstrated 
is probably chiefly due to secreting glands in the 
mucous membrane. If the " secretion current " 
is compensated after the general compensation 
method described on page 294, and the glosso- 
pharyngeal nerve then stimulated, the electrom- 
eter will show an electromotive force, in a 
direction opposite to the original difference of 
potential, — in other words, a " negative variation." 

Negative Variation of Secretion Current. — Place 
a frog curarized until voluntary motion is just 
paralyzed back uppermost on the frog board. 
Strip the skin from one thigh, and expose 

21 



322 THE OUTGO OF ENERGY 

the sciatic nerve of this side. Place non-polar- 
izable electrodes on the bare muscle of the 
thigh and on the skin of the leg. Connect the 
electrodes to a rheochord arranged for compensa- 
tion by the bridge method, as shown in Fig. 47. 
Place the capillary electrometer in a short cir- 
cuit. Bring the meniscus into the field, and 
note its position. Open the short-circuiting key. 
Move the slider along the wire until the meniscus 
returns to its original position. Now stimulate 
the sciatic nerve with the tetanizing current. 

A negative variation will be seen. If the skin 
current was slight, the variation may be positive. 

The greater part of the skin current is doubt- 
less a secretion current, but not all. Weak cur- 
rents have been obtained from skin devoid of 
glands, for example, the eel's skin. Hermann 
attributes this current to the degeneration which 
accompanies the change of the nucleated cells of 
the corium to the dead scales of the outer 
epidermis. 

A strong secretion current may be obtained 
from the skin of the foot (cat). On stimulation 
of the sciatic nerve, the current is increased 
(positive variation). 

In the submaxillary gland, the hilus is positive 
to any point on the external surface of the gland. 
Stimulation of the chorda tympani nerve, secre- 



THE ELECTROMOTIVE PHENOMENA 323 

tory fibres from which are supplied to the gland, 
causes the surface to become still more negative, 
i. e. the secretion current is increased (positive 
variation). Stimulation of the sympathetic, which 
also sends fibres to the gland, causes the secretion 
current to lessen (negative variation). 

Electrotonic Currents 

It has already been shown that the irritability 
and conductivity of the nerve are altered by the 




Fig. 55. 

galvanic current. So also are the electromotive 
properties. 

Place one pair of non-polarizable electrodes 
near the middle of a long piece of extirpated 
nerve, and one other pair at each end, on the 
cross-section and longitudinal surface as in Fig. 
55. Connect the middle pair through a key 
with two dry cells. Connect each of the other 
pairs through a short-circuiting key with a 



324 THE OUTGO OF ENERGY 

capillary electrometer. Let one observer watch 
each meniscus, while a third experimenter 
manages the polarizing current. Note the posi- 
tion of each meniscus. Open the short-circuiting 
keys. In each electrometer, the meniscus will he 
displaced by the demarcation current. It should 
be noted that the demarcation currents are of 
opposite direction, flowing in the nerve from the 
cross-section towards the longitudinal surface. 
Make the polarizing current. 

When the polarizing current enters the nerve, 
there will be a twitch in each electrometer, 
caused by the negative variation of the demar- 
cation current; this may be neglected. Each 
meniscus will be displaced; on the side of the 
anode of the polarizing current, the demarcation 
current will be reinforced, but on the side of the 
cathode it will be diminished. 

Thus the passage of the galvanic current 
through a part of the nerve has polarized the 
nerve on both sides of that part. The extra- 
polar region on the side of the anode becomes 
positive ; the extrapolar region on the side of the 
cathode becomes negative ; similar changes prob- 
ably occur in the intrapolar region. In short, an 
electrotonic current is set up, having the same 
direction as the polarizing current. This electro- 
tonic current augments the demarcation current 



THE ELECTROMOTIVE PHENOMENA 325 

on the side of the anode, but is opposed to that 
on the side of the cathode. It appears when 
any two points on the longitudinal surface are 
" led off " to the electrometer, and is entirely 
independent of the demarcation current. 

The intensity of the electrotonic current de- 
pends on the intensity of the polarizing current. 
The greater the separation of the polarizing elec- 
trodes, the less the electrotonic effect, as might be 
expected from the great resistance of nerve. If 
this factor be excluded by placing in the circuit 
a much greater resistance than that of nerve, the 
electrotonic effect will be found to increase with 
the length of the intrapolar region. The electro- 
tonic current is absent in dead nerves, in strongly 
cooled nerves, and in those ligated between the 
polarizing electrodes and the electrodes leading 
to the electrometer. 

In muscle, the electrotonic currents are much 
stronger than in nerve. 

Negative Variation of Electrotonic Currents ; 
Positive Variation (Polarization Increment) of Polar- 
izing Current. — Place the polarization electrodes 
near one end of the nerve. Connect them through 
a short-circuiting key with a dry cell. From the 
short-circuiting key lead to a capillary electrom- 
eter (Fig. 56). From the middle of the nerve 
lead off the electrotonic current through a short- 



326 THE OUTGO OF ENERGY 

circuiting key to a second capillary electrometer. 
Near the other end of the nerve place stimu- 
lating electrodes connected with the secondary 
coil of an inductorium arranged for tetanization. 
Make the polarizing current. Open the short- 
circuiting key leading to the electrotonic elec- 
trometer, and note the position taken by the 
meniscus under the influence of the electrotonic 
current. Make the tetanizing current. 

a 






p* 3 

JL_ If U. 

Fig. 56. 

The strength of the electrotonic current will 
be diminished. At the same time the strength 
of the polarizing current will be increased (polar- 
ization increment). 

These are in reality action currents. 

The electrotonic currents are absent in nerves 
which lack a myelin sheath. This suggests that 
the myelin in some way divides the nerve into a 
core and a sheath. If a zinc wire connecting 
two electrodes is surrounded by a layer or sheath 



THE ELECTROMOTIVE PHENOMENA 327 

of saturated solution of sulphate of zinc, there 
will be no polarization, and the current will not 
spread to any extent beyond the electrodes. If, 
however, the wire is platinum instead of zinc, 
polarization will take place where the current 
passes from the electrodes through the electrolyte 
into and out of the wire, and the polarization 
may be recognized by connecting the extrapolar 
region with the electrometer as in the foregoing 
experiment. The resistance to the spread of the 
electrotonic current in a longitudinal direction is 
relatively slight, so that it passes almost instantly 
along the core. 

In nerve, also, the greater resistance in the 
transverse direction (five-fold greater than the 
resistance in the longitudinaj. direction) would 
favor the spread of electrotosiic currents length- 
wise along the nerve. 

Certain observations of Biedermann make it 
difficult to accept without reservation the simple 
physical explanation just offered. For example, 
the narcotization of a nerve with ether or chloro- 
form causes the electrotonus to disappear a 
short distance from the electrodes, although 
still strongly present in their immediate neigh- 
borhood. These experiments cannot be discussed 
here, but they indicate that to the purely physi- 
cal must be added a physiological electrotonus. 



328 THE OUTGO OF ENERGY 

The Electrotonic Current as a Stimulus. — As 

would naturally be expected, the electrotonic 
current may be an effective stimulus. Bring the 
end of an extirpated nerve A into contact with 
the distal portion of the nerve of a nerve-muscle 
preparation, B, as in Fig. 57, and place on the 
other end of A non-polarizable electrodes joined 
through a key to a battery of two cells. Make 
the galvanic current. 
Muscle B will contract. 

The galvanic current polarizes nerve A, and 
the electrotonic current thereby 
set up passes into the nerve of 
B through the contact, and occa- 
sions in nerve B an impulse 
which descends to the muscle 

jng. vt. 

and stimulates it to contract. 

Paradoxical Contraction. — Expose the bifur- 
cation of the sciatic nerve into tibial and peroneal 
branches. Polarize either of these branches. 
(The electrodes should not be placed too near 
the bifurcation.) 

On making and breaking the polarizing cur- 
rent, the muscles supplied by each branch will 
contract. 

In this instance, the extrapolar region of the 
branch polarized lies in part in the main trunk. 
The electrotonic current there spreads into the 




THE ELECTROMOTIVE PHENOMENA 329 

contiguous axis cylinders, among them those 
of the other branch. 



Electric Fish 

There are several species of fish which possess 
the power of discharging electrical currents when 
stimulated. The best known are Torpedo, a ray 
found on the coasts of Europe ; Gymnotus, the 
electrical eel of South America ; and Malapteru- 
rus electricus, a catfish found in the Nile and 
other African rivers. The electromotive force of 
these fishes is derived from a special organ placed 
beneath the skin. This electrical organ is bilat- 
eral and is formed of parallel plates. One side 
of each plate receives a branch of the electrical 
nerve, which in Malapterurus is a single great 
axis cylinder derived from a giant nerve cell. 
The side of the plate receiving the nerve becomes 
negative to the other side when the electrical 
organ is active ; it behaves like the negative plate 
of the ordinary cell. When the nerve is at rest, 
there is no difference of potential in the electrical 
organ. The discharge in the active state is peri- 
odic, and may rise to 200 per second. The elec- 
tromotive force is considerable : in Torpedo, 30-35 
volts, 5 volts for each cubic centimetre of the 
organ, 0.08 volt for each plate. The fish itself 



330 THE OUTGO OF ENERGY 

is not injured by the current ; its tissues are 
not easily excitable by electricity, though they 
respond readily to mechanical stimulation. 

Apparatus 

Normal saline. Bowl. Towel. Pipette. Glass plate. 
Sharp knife. Two dry cells. Four non-polarizable elec- 
trodes. Simple key. Capillary electrometer. Co-ordi- 
nate paper. Millimetre scale. Inductorium. Electrodes. 
Thirteen wires. Porcelain dish. Muscle clamp. Muscle 
lever. Stand. Cork. Rheochord. Normal saline clay. 
Filter paper. Wheel interrupter. Candle-wick. Electro- 
magnetic signal. Pole-changer. Bent hooks. Black paper 
(stroboscope). Moist chamber. Large and small brass 
electrodes. Cotton. Common salt. Two beakers. Satu- 
rated solution of zinc sulphate. Cotton thread. Frog 
board. Heart-holder. Black box for covering retina. 
Bunsen burner. Glass slide. Cork clamp. Frogs. 



THE CHANGE IN FORM 331 



III 

THE CHANGE IN FORM 

The change in form or the contraction of muscle 
is the most conspicuous of the several ways in 
which its energy is set free. It has already been 
shown that this change consists of a shortening 
of the contractile mass followed by a return to 
the original length. It is necessary now to de- 
termine whether the muscle becomes smaller on 
entering the active state or whether the altera- 
tion in form is simply a shifting — a transloca- 
tion — of the muscular units. 

Volume of Contracting Muscle 

Strip the skin from the hind limb of a frog. 
Hang the limb from the hooked electrode in the 
stopper of the volume tube (Fig. 58) and place 
the stopper loosely in the tube. Hook the elec- 
trode at the other end of the tube into the limb 
near the foot. Fill the tube absolutely full of 
boiled normal saline solution, slightly withdraw- 
ing the stopper for the purpose. Replace the 
stopper in the tube in such a way that all air 



332 



THE OUTGO OF ENERGY 



bubbles shall be excluded. If the height of the 
water-column in the capillary tube 
does not permit the meniscus to be 
readily observed, move the glass rod 
in the stopper in or out until the 
meniscus is adjusted. Connect the 
electrodes with the secondary coil 
of an inductorium arranged for 
single induction currents. Note 
carefully the level of the water in 
the capillary tube. Stimulate the 
muscle with a maximal break 
current. 

The level of the water in the 
capillary will not change. The 
change in the form of the contracting muscle 
is not accompanied by a change in volume. 1 




Fig. 58. The 
volume tube. 



The Single Contraction or Twitch 

The change in the form of the muscle on 
entering the active state is usually studied from 
the graphic record made on a smoked surface 
by a writing lever the shorter arm of which is 
attached to the end of the muscle. Such a 
record, it should be remarked, gives the extent 

1 This experiment must not be regarded as excluding a very 
slight change in volume, because of the difficulty of expelling, 
by boiling or otherwise, all the air in the saline solution. 



THE CHANGE IN FORM 333 

and the time relations of the shortening, but not 
the thickening of the muscle. (See page 339.) 

The Muscle Curve. Prepare a gastrocnemius 
muscle together with the distal third of the 
femur. Fasten the latter in the muscle clamp. 
Attach the tendo Achillis to the hook on the 
muscle lever by means of a fine copper wire 
which should be wrapped round the hook and 
the end then carried to the binding post on the 
muscle lever. Place a ten-gram weight in the 
scale-pan. Connect the posts on the clamp and 
the lever with the secondary coil of an inducto- 
rium arranged for maximal induction currents. 
In the primary circuit place an electromagnetic 
signal. Bring the writing points of the signal 
and the muscle lever against the smoked paper 
in the same vertical line. Start the drum at its 
most rapid speed. Stimulate the muscle with a 
maximal break current. 

The muscle will shorten and then extend, 
marking a period of rising energy and a period 
of sinking energy. Note that the period of rising- 
energy is shorter than the period of sinking 
energy. Close observation will show that the 
lever does not begin to move at the instant the 
muscle is stimulated, — there is here an interval 
or latent period. 

The Duration of the Several Periods. — Turn to 



334 THE OUTGO OF ENERGY 

the right the screw at the top of the sleeve bear- 
ing the recording drum until the sleeve is raised 
from the friction bearing. The drum can now 
be "spun." Start the tuning fork vibrating, 
spin the drum, lay the writing point of the tun- 
ing fork on the smoked paper near the line 
traced by the electro-magnetic signal, and stim- 
ulate the muscle with a maximal induction 
current. 

An interval will be found between the moment 
of stimulation (marked by the electromagnetic 
signal) and the beginning of contraction. This 
interval is the mechanical latent period. Meas- 
ure its duration by means of the tuning fork 
curve. Measure also the duration of the period 
of rising energy and the period of sinking energy. 

Helmholtz, who first measured the latent period 
of frog's muscle, found a mean duration of 0.01 
sec, while the phase of rising energy measured 
0.04 sec, and the phase of sinking energy 0.05 
sec. More recent measurements by Tigerstedt 
and others have reduced the latent period 
given by Helmholtz to from 0.0025 to 0.005 
sec. The interval observed grows less as the 
intensity of stimulation is increased from the 
threshold to the maximal value ; further in- 
crease in intensity (supermaximal stimulation) 
causes no further diminution in the latent period. 



THE CHANGE IN FORM 335 

The period is shorter at high temperatures than 
at low, with maximal break induction currents 
than with make induction currents, with break 
induction currents than with closure of the gal- 
vanic current. Changing the load of the muscle 
is without effect on the latent period. 

When the muscle is stimulated through its 
nerve the latent period is longer by about 0.002 
sec. than when the electrodes are placed on the 
muscle itself (Bernstein), due allowance being 
made for the time occupied by the passage of 
the nerve impulse along the trunk of the nerve 
from the point of stimulation to the muscle. The 
additional time is taken perhaps in the passage 
of the impulse through the end plate into the 
contractile substance. 

Grutzner has shown that the striated muscle 
fibres, particularly of vertebrates, differ in their 
histological elements. Some are rich in sarco- 
plasm, and when seen by transmitted light appear 
cloudy and granular ; others have less sarcoplasm 
and are relatively translucent. This difference 
in structure is associated with a striking differ- 
ence in the character of the contraction. The 
muscles composed chiefly of turbid fibres contract 
slowly, while " clear " muscles contract rapidly 
(compare page 178)! Thus in the rabbit the 
duration of the contraction of the red sulcus 



336 THE OUTGO OF ENEKGY 

muscle, which is rich in sarcoplasm, is about 
1.0 sec, while in the white gastrocnemius — a 
"clear" muscle — it is 0.25 sec. In the frog, the 
contraction period of the hyoglossus is 0.205, 
the gastrocnemius 0.120, and the gracilis 0.108 
sec. (Cash). The latent period is longer in the 
red muscles. The amplitude of contraction is 
less in the red than in the white. 

The mixture of quickly and slowly contracting 
fibres in the same muscle is sometimes obviously 
an advantage. Thus in certain bivalves the quick 
fibres in the shell-closing muscle close the shell 
rapidly, and the slow fibres keep it closed after 
the contraction of the quick fibres has ceased. 

The form of the contraction is influenced by 
the mixture of fibres. The clear fibres reach 
their maximum shortening sooner than those 
rich in sarcoplasm. In some instances, indeed, 
the contraction curve may show two summits. 
These differences may perhaps explain the char- 
acteristic differences in the form of the contrac- 
tion wave of different muscles, observed by Cash 
and others. The white fibres are more easily 
fatigued than the red. Thus the triceps humeri 
of the rabbit contracts at the beginning of stimu- 
lation like an unmixed white muscle (quickly), 
but later like a red muscle (slowly). 

The Excitation Wave. — Prepare a plate of 



THE CHANGE IN FORM 337 

cork one inch long and just narrow enough to be 
held in the Gaskell clamp (Fig. 26). Smoke a 
drum. Raise the drum off the friction bearing 
by turning to the right the milled screw at the 
top of the shaft. Fasten the end of a curarized 
sartorius muscle to the cork plate by means of 
two needles to the ends of which conducting 
wires are soldered. Place the preparation in the 
Gaskell clamp in such a way that the clamp 
shall compress the equator of the muscle suffi- 
ciently to prevent the passage of a contraction 
wave from one part of the muscle to the other, 
but not sufficiently to prevent the passage of the 
excitation. Let a second pair of needle elec- 
trodes rest on the muscle near the upper side of 
the clamp. Fasten the clamp to the iron stand. 
Connect the two pairs of electrodes to the end 
cups of a pole-changer (without cross-wires), the 
side cups of which are connected with the secon- 
dary coil of an inductorium arranged for single 
maximal induction currents. In the primary 
circuit of the inductorium place the electro- 
magnetic signal. Fasten the tibial end of the 
muscle to a muscle lever. Bring the writing 
point against the smoked surface exactly under- 
neath the point of the electro-magnetic signal. 
" Spin " the drum slowly. Place the writing 
point of a vibrating tuning fork against the 
22 



338 THE OUTGO OF ENERGY 

smoked paper below the recording levers. Stim- 
ulate the muscle with a maximal break current 
first through one pair of electrodes and then 
through the other. In each of the resulting 
curves measure the interval between stimulation 
and contraction (for method see page 184). 

This interval will be longer when the muscle 
is stimulated farther from the portion the con- 
traction of which is recorded. The difference is 
the time taken by the excitation to traverse the 
part of the muscle lying between the two pairs 
of electrodes. Measure the distance and calcu- 
late the speed of the excitation. 

The nature of the excitation process is un- 
known. The current of action has been shown 
to precede the visible change in form of muscle. 
It is usually assumed to be a manifestation of the 
excitation process, but the precise relation be- 
tween the two has never been ascertained. The 
speed of the excitation is the same as that of the 
contraction wave. 

The Contraction "Wave. — Eemove from a CU- 
rarized frog the long parallel-fibred muscles ex- 
tending along the inner side of the thigh from 
the pelvis to the tibia. Let the preparation rest 
horizontally on a glass plate supported on a stand. 
With fine wire fasten near the axle of each of 
two heart levers a small piece of cork into which 



THE CHANGE IN FORM 339 

the point of a long pin has been thrust. Place 
the levers so that the head of the first pin rests 
on the muscle near one end, while the head of 
the second pin rests near the other end. Place 
needle electrodes at one end of the muscle. 
Bring the writing points of the two levers 
against a smoked drum in the same vertical line. 
Let a tuning fork write its curve near that of the 
muscle levers. Set the tuning fork vibrating. 
Let the drum revolve rapidly. Stimulate the 
muscle at one end with a maximal make induc- 
tion current. 

The lever near the point of stimulation will 
begin to rise before that farther away. Evidently 
the contraction starts at the point stimulated and 
spreads along the muscle in the form of a wave 
(compare pages 308 et seq.). 

Determine the speed per second of the wave 
of contraction by measuring with the tuning-fork 
curve the time occupied by the wave in passing 
along the muscle from one lever to the other. 

It is evident that a lever resting on a horizontal 
muscle will register the change in form of the 
cross-section on which the lever lies, while a lever 
attached to the end of a muscle suspended verti- 
cally will be moved by the change in form of all 
the cross -sections of which the muscle is com- 
posed. The curves secured by the two procedures 



340 THE OUTGO OF ENERGY 

are similar in form, but different in duration. 
The curve of thickening is shorter by the differ- 
ence between the time taken by the contraction 
wave to pass over the single cross-section, on the 
one hand, and the whole length of the muscle on 
the other. 

An extirpated muscle is apt to remain short- 
ened after contraction. To bring muscles back 
to their original length it is usually necessary to 
weight them, or — as in the body — to submit 
them to the pull of antagonists. Even the 
weighted muscles may return very slowly and 
imperfectly to their normal length. This con- 
tracture, as it is termed, is seen especially in 
strong direct stimulation, in poisoning with vera- 
trine, and as death comes on. Contracture is 
not the result of fatigue, for when the muscle 
is repeatedly stimulated contracture diminishes, 
instead of increasing. During contracture, the 
irritability of the muscle for stimulation through 
the nerve is diminished. 

Relation of Strength of Stimulus to Form of 
Contraction "Wave. — Fasten the femur of a gas- 
trocnemius preparation in the muscle clamp and 
attach the Achilles tendon to the muscle lever 
with a fine copper wire the end of which should 
be carried to the binding post on the handle of 
the lever. Connect this post and that on the 



THE CHANGE IN FORM 341 

muscle clamp with the secondary coil of the in- 
ductorium. Bring the writing point against the 
smoked drum. Stimulate the muscle with break 
induction currents of varying intensity and record 
the contraction curves. 

It will be found that the contraction is longer 
with weak stimuli than with strong. 

Influence of Load on Height of Contraction. — 
Attach a curarized gastrocnemius preparation 
to the muscle lever and bring the writing point 
against a smoked drum. Connect the binding 
posts on the lever and the muscle clamp with 
the secondary coil of the inductorium. Load 
the muscle with the lever and scale-pan only. 
With the drum at rest record the contraction 
on stimulation with a maximal induction current. 
Turn the drum by hand one millimetre. Place 
a one-gram weight in the scale-pan, and record 
the contraction produced by a make induction 
current of the same intensity as before. Con- 
tinue to add oram weights and to record the 
contractions until ten one-gram weights have 
been placed in the scale-pan. Now increase the 
load each time by ten grams, recording the con- 
traction after each increase, until the muscle is 
weighted witli one hundred grams. (Care should 
be taken not to fatigue the muscle by stimulating 
it oftener than is necessary to obtain the record.) 



342 THE OUTGO OF ENERGY 

Within certain narrow limits the height of the 
contraction will be increased by the increase in 
the load. With increasing loads the height of 
contraction diminishes at first quickly, and then 
more slowly. 

Influence of Temperature on the Form of the 
Contraction. — Prepare a gastrocnemius muscle 
together with its attachment to the femur. 
Fasten the femur in the " muscle warmer " (Fig. 
59). Tie the end of a fine copper wire about 
ten centimetres long around the Achilles tendon. 
Bring the wire through the opening in the muscle 
warmer and fasten the wire around the pulley 
of the muscle lever. If the pulley is of metal 
the muscle lever should be supported on a stand 
separate from that bearing the muscle warmer 
or should be otherwise insulated. Connect the 
muscle warmer and the muscle lever with the 
secondary coil of an inductorium arranged for 
single induction currents. Fill a beaker with 
cracked ice and add a little salt. Immerse the 
muscle warmer in the beaker and support the 
latter on a suitable stand. Bring the writing 
point of the muscle lever against a smoked 
drum. Let the drum revolve at fairly rapid 
speed. Stimulate the cooling muscle at inter- 
vals of 5° with a maximal break current. 



THE CHANGE IN FORM 



343 



The Muscle Warmer. 1 — A disk, supported by a 
rod, bears three pins (Fig. 59). One of the three pins 
is prolonged and bent at a right angle near its lower 
end. To the bend is fas- 
tened one end of the mus- 
cle under experimentation. 
About the other end is tied 
a fine copper wire which 
passes through a hole in 
the disk to reach a muscle 
lever. A second opening in 
the disk is provided with a 
short metal tube, in which 
a thermometer is held by 
a piece of rubber. The 
bulb of the thermometer 
may be placed on a level 
with the belly of the 
muscle. When these ad- 
justments are complete, a 
glass cylinder is brought 
against the under surface 
of the disk, where it is held 
in position by the "spring" of the three pins. A 
beaker or other vessel containing water is now 
placed beneath the cylinder and raised until the 
cyclinder is sufficiently immersed. The temperature 
of the muscle is altered by heating or cooling this 




Fig. 59. The muscle warmer ; 
an apparatus for studying the in- 
fluence of temperature on mus- 
cular contraction. 



1 American Journal of Physiology, 1904, x, p. xliii. 



344 THE OUTGO OF ENERGY 

water. Direct electrical stimulation of the muscle 
may be made by connecting one electrode with the 
metal parts of the apparatus and the other with the 
copper wire attached to the upper end of the muscle. 

Xote that as the temperature falls the contrac- 
tion curve becomes longer. The phase of rising 
energy is lengthened more than the relaxation. 
The earlier portion of the relaxation is lengthened 
less than the later ; the muscle shows a tendency 
to contracture (see page 340). 

Place fresh paper on the drum. Let the drum re- 
volve very slowly. Place a lighted Bunsen burner 
under the arm of the muscle warmer. At intervals 
of 5° stimulate the muscle with a maximal break 
current. Xote the changes in the contraction. 

The height of contraction is least at the freezing 
point of the muscle (-5°). It rises from the 
freezing point to 0°; falls from 0° to 19°; in- 
creases to 30°, which is the maximum ; from 30° 
to 45° diminishes again; and at 45° the frog's 
muscle usually enters into a state called rigor 
caloris; the muscle becomes opaque, inelastic, 
resistant to the touch, shortens very considerably, 
and undergoes chemical changes of great impor- 
tance. The duration of contraction lessens witli 
the rising temperature, being least at 30°. Above 
30° the duration remains approximately un- 
changed. The latent period is increased at low 



THE CHANGE IN FORM 345 

temperatures, diminished at high. Above 30° the 
excitability to electrical stimuli diminishes stead- 
ily ; it disappears almost entirely before rigor is 
reached. 

Influence of Veratrine on the Form of the Con- 
traction. — With a capillary pipette inject in the 
dorsal lymph sac 5 drops of a 1 per cent solution 
of veratrine sulphate or acetate. After a few 
minutes, test for symptoms of veratrine poisoning 
by pinching the foot from time to time. 

Soon the mechanical stimulation will be fol- 
lowed by prolonged contraction of the extensor 
muscles and still more prolonged relaxation. 

Make a gastrocnemius muscle preparation. 
Fasten the muscle to a muscle lever and bring the 
writing point against a smoked drum. Eecord a 
single contraction. 

Note the increased height of the phase of 
shortening, and the prodigious increase in the 
duration of the phase of relaxation. This con- 
tracture (page 340) is lessened by repeated stimu- 
lation, but reappears if the muscle be allowed 
to rest. Cooling or warming usually causes the 
veratrine effect to disappear temporarily. 

A quick initial contraction may precede the 
characteristic veratrine contraction, possibly be- 
cause the veratrine affects differently the red and 
the clear fibres. 



346 THE OUTGO OF ENERGY 



Tetanus 

Superposition of Two Contractions. — Arrange 
a gastrocnemius muscle to write on a smoked 
drum. Connect the binding posts on the muscle 
lever and muscle clamp with the secondary coil 
of an inductorium. In the primary circuit (posts 
1 and 2) place the electro-magnetic signal and a 
simple key. Let the drum revolve at a rapid 
rate. Send two maximal induction currents 
through the muscle at varying intervals, begin- 
ning with the shortest interval possible. The 
secondary should be at such a distance from 
the primary coil that both make and break cur- 
rents shall cause maximal contraction. 

If the second stimulus fall in the latent period 
of the first contraction, the stimulus will be with- 
out effect. If the second stimulus fall between 
the beginning of shortening and the end of relax- 
ation caused by the first stimulus, the contraction 
following the second stimulus will not begin from 
the base line, but will be superposed on the first, 
as if the state of shortening from which the 
second contraction begins were the resting stage 
of the muscle. The height reached by the 
second contraction will be greater than that 
reached by the first. The summed height is 



THE CHANGE IN FORM 347 

usually greatest when the second contraction 
starts from the summit of the first, but this rule 
is not invariable. The summit of the summed 
contraction does not necessarily coincide with the 
summit of the second contraction ; the higher the 
summed contraction, the quicker the summit is 
reached. 

Superposition in Tetanus. — Place the vibrat- 
ing interrupter (Fig. 50) in the primary circuit. 
Eepeat the preceding experiment, but use a series 
of stimuli instead of only two. It will be ob- 
served that a third contraction may be super- 
posed on the second, a fourth on the third, and 
so on. The shortening of muscle, however, has a 
limit; and when this is reached, further stimu- 
lation merely maintains this maximum degree of 
shortening until fatigue sets in. When the in- 
terval between successive stimuli is very brief 
the successive contractions appear to fuse to- 
gether and the contraction curve becomes a con- 
tinuous line. The more rapid the contraction, 
the shorter must be the interval between succes- 
sive stimuli in order to cause the disappearance 
of the individual contractions. Thus a more 
rapid rate of stimulation is necessary to produce 
complete fusion in fresh, highly irritable muscles 
than in those the irritability of which has been 
diminished by cold or fatigue. For this reason 



348 THE OUTGO OF ENERGY 

contractions which at the beginning of the stim- 
ulation period are marked by notches in the curve 
fuse completely as longer stimulation brings on 
fatigue. Here also the differences in the structure 
of muscles already mentioned play an important 
part. Thus the red muscles of the rabbit are 
thrown into tetanus by a much smaller number 
of stimuli per second than are the more quickly 
contracting white muscles. 

Relation of Shortening in a Single Contraction 
to Shortening in Tetanus. — 1. Eecord side by 
side the contractions of a muscle unloaded except 
by the muscle lever. Stimulate with a single 
maximal induction current ; stimulate with a 
brief tetanizing current. 

The shortening of the single twitch of the un- 
loaded muscle is as great as the shortening in 
tetanus. 

2. Load the muscle with ten grams and repeat 
Experiment 1. 

The shortening in tetanus will now be con- 
siderably greater than that of the single twitch. 

3. Load the muscle with ten grams but sup- 
port the weight by the after-loading screw, so 
that the weight cannot pull on the muscle until 
the contraction begins. Eecord one contraction 
on a stationary drum in response to a maximal 
make induction current. Turn the drum one 



THE CHANGE IN FORM 349 

millimetre. Eaise the writing point of the lever 
one millimetre by means of the after-loading 
screw. Stimulate the muscle with a make in- 
duction current of the same intensity as before. 
Again turn the drum and raise the point of the 
lever one millimetre, and stimulate the muscle 
as before. Continue this until the after-loading 
screw is raised so high that the muscle no longer 
shortens sufficiently to raise the lever. 

Obviously in this experiment the weight is arti- 
ficially supported during a progressively greater 
portion of the contraction. It will be found that 
the total shortening of the muscle loaded only 
during the latter portion of the contraction is 
as great as the shortening of a loaded muscle in 
tetanus. 

The Isometric Method 

Thus far we have observed the development 
of energy in a muscle stretched by a small, un- 
varying load. The principal part of the energy 
set free in this isotonic process appears as the 
mechanical energy of a visible change in form ; 
a small part of the energy of the muscle is con- 
verted into tension. Fick has pointed out that 
if the muscle be made to pull against a strong 
spring, the change in the length of the muscle 



350 THE OUTGO OF ENERGY 

will be very slight, and the greater portion of the 
energy will be converted into tension and stored 
in the spring. If the excursion of the spring be 
recorded by a writing lever, the curve will be 
practically a record of the course of transforma- 
tion of energy into tension, and will be only to a 
slight extent the record of a change in form. 

In order to determine the amount of energy 
converted into tension in the isometric contrac- 
tion, it is necessary to graduate the spring against 
which the muscle pulls. 

Graduation of Isometric Spring. — Attach the 
large scale-pan to the strong spring of the appa- 
ratus shown in Fig. 60. Place a long straw on 
the end of the spring. Bring the writing point 
against the smoked paper of a kymograph. Turn 
the drum once round to record an abscissa. Ee- 
turn the drum to its former position, and place 
80 grams in the scale-pan attached to the spring. 
When the spring is stretched turn the drum once 
round to record the bending under 100 grams' 
weight. 1 Restore the drum to its former posi- 
tion, add 100 grams, and make record of the 
extension at 200 grams. Continue the record 
up to 1000 grams. Preserve the curve for ref- 
erence (page 363). 

i The scale-pan weighs about 20 grams. 



THE CHANGE IN FOKM 



351 



The Heavy Muscle 
Lever. 1 — It is sometimes 
necessary to after-load a 
muscle lever with weights 
far in excess of those that 
a light muscle lever will 
bear without "springing" 
and thus altering the ab- 
scissa. Such heavy loads 
are borne by the heavy 
muscle lever illustrated in 
Fig. 60. A tripod of ja- 
panned malleable iron, 27 
cm. high and 17.5 cm. 
broad at the base, supports 
a femur clamp and a mus- 
cle lever. The latter is 
a steel tube 5 cm. long, 
pierced by a steel axle 9 mm. 
long, revolving between 
heavy brass posts. The 
lever weighs about 2.5 gms. 
The aluminium scale-pan 
weighs about 20 gms. ; it 
holds one hundred 10-gram 
weights. The lever may be 
turned completely over in 
a backward direction, and 




The heavy muscle 



1 American Journal of Physiology, 1903, viii, p. xl. 



352 THE OUTGO OF ENERGY 

thus be entirely out of the way. The steel spring 
shown upon the left of Fig. 60 may then be turned to 
the right to bring its wire hook into the opening 
through which the scale-pan is reached. The scale- 
pan may then be attached to this isometric spring and 
the spring empirically graduated. When the gradua- 
tion scale has been written, the milled screw that 
holds the isometric spring upon the left-hand post 
(Fig. 60) may be loosened, the spring turned with the 
hook up, and the screw made fast again. The lower 
end of the muscle may now be attached to the 
hook upon the spring and an isometric curve written. 

The screw clamp holding the muscle clamp is 
insulated. A binding post upon the muscle clamp, 
and another binding post upon the right-hand post 
supporting the axle of the lever, allow direct stimula- 
tion of the muscle. 

This lever serves especially well for the double 
abductor preparation of Fick, consisting of the semi- 
membranosus and gracilis of both sides. 

Isometric Contraction. — Invert the spring. 
Fasten the femur of a gastrocnemius preparation 
in the muscle clamp, and the Achilles tendon to 
the spring. • Connect the binding posts on the 
lever and the clamp with the secondary coil of the 
inductorium, arranged for single maximal induc- 
tion currents. Let the drum revolve at a rapid 
speed. Stimulate the muscle with a maximal 
break current. 



THE CHANGE IN FORM 353 

An isometric contraction will be recorded. 

Eemove the spring, and attach the tendon to 
the lever weighted with ten grams. Stimulate 
the muscle with a break induction current of the 
strength used before. 

The usual isotonic curve will be written. 
Comparison of the isometric and isotonic curves 
reveals as a rule in the isometric curve a longer 
phase of rising energy and a flattened summit 
or plateau. The muscle reaches its maximum 
tension sooner than its maximum shortening and 
maintains the maximum tension longer than the 
maximum shortening. 

Contraction of Human Muscle 

Simple Contraction or Twitch. — Place the 
middle, ring, and little fingers in the support of 
the ergograph (Fig. 61). Let the adjustable rod 
rest on the index finger near the distal end of 
the middle phalanx. Place the point of the rod 
in the hole nearest the free end of the spring. 
Adjust the writing point to write on a smoked 
drum revolving at moderate speed. With the brass 
electrodes covered with wet cotton (page 129), 
stimulate the abductor indicis with a single max- 
imal break induction current. Compare the form 
of the curve thus obtained with the contraction 
curve of the skeletal muscle of the frog. 
23 



354 



THE OUTGO OF ENERGY 



The Ergograph. 1 — A flat, steel spring provided 
with a writing point is fastened in a stout iron support 
clamped to the table (Fig. 61). The second, third, and 
fourth fingers of the subject's hand are fastened with 
tapes to the wooden support, Upon the index finger 




Fig. 61. The ergograph; also employed for recording the isometric and 
isotonic contractions of human muscle. 



near the distal end of the middle phalanx is placed a 
rod the length of which is adjustable. The point of 
the rod passes through a rubber ring and presses 
against the under side of the spring. "When the point 

1 First described in the " Introduction to Physiology/' 1901, 
p. 220. 



THE CHANGE IN FORM 355 

is near the free end of the spring, contractions of the 
abductor indicis muscle with voluntary and electrical 
stimuli may be recorded. When the point of the 
rod is placed near the cast-iron support of the spring, 
the movements of the spring will be so much less that 
almost none of the energy of the muscle will be con- 
verted into mechanical motion. An isometric con- 
traction will be recorded. 

Isometric Contraction. — Place the point of the 
adjustable rod in the hole nearest the cast-iron 
support of the spring. The movement of the 
spring is so much less at this point that almost 
none of the energy of the muscle will be con- 
verted into mechanical motion. Stimulate the 
muscle as before with a maximal break induc- 
tion current. Compare the isometric curve thus 
recorded with the largely isotonic curve previ- 
ously obtained. 

Artificial Tetanus. — Eeplace the adjustable rod 
in its former position (isotonic arrangement). 
Stimulate the abductor with the tetanizing cur- 
rent of the inductorium. Compare the curve 
with the tetanus of frog muscle. 

Natural Tetanus. — 1. Contract the abductor 
by voluntary impulse. This also gives a tetanus 
curve. When the natural tetanus is prolonged. 
it frequently is marked by oscillations having a 
periodicity of about ten per second. 



356 THE OUTGO OF ENERGY 

2. Place the adjustable rod in the hole nearest 
the iron support (isometric arrangement). Stimu- 
late the muscle (1) with the tetanizing current 
of the inductorium ; (2) by voluntary impulse. 

It will be seen that the energy set free by the 
natural stimulus is much greater than when the 
muscle is stimulated artificially. 

Smooth Muscle 

Spontaneous Contractions. — Make two cuts, 
5 mm. apart, through the frog's stomach at 
right angles to the long axis. Pass a bent hook 
through the ring (i. e. through the cavity of the 
stomach), and fasten the hook in the muscle 
clamp. Pass a second hook around the lower 
margin of the ring and attach it by means of a 
fine copper wire to the straw of the heart lever 
(Fig. 53). Contraction of the circular fibres can 
thus be made visible. Bring the writing point 
against a drum revolving about once an hour. 
Wrap filter paper saturated with normal saline 
solution about the muscle ring. Keep this 
thoroughly moist. Proceed to the remaining ex- 
periments, observing the stomach preparation 
from time to time. 

Spontaneous rhythmic contractions will appear. 
Note the changes in tonus. 



THE CHANGE IN FOEM 357 

Simple Contraction. — Prepare a second ring 
of frog's stomach in the manner described in 
the preceding experiment. Attach the lower 
margin of the ring to the muscle lever by means 
of a fine copper wire. Carry the end of the 
copper wire to the binding post on the muscle 
lever. Connect this post and the post on the 
muscle clamp with a dry cell, interposing a sim- 
ple key. Place the electro-magnetic signal in the 
primary circuit. Bring the writing points of the 
muscle lever and the signal against a smoked 
drum in the same verticle line. Let the drum 
move at slow speed. Stimulate the muscle by 
making and breaking the galvanic current once, 
not oftener. 

Compare the duration of the latent period with 
that of skeletal muscle. Compare the form of 
the contraction curve with that of skeletal 
muscle. 

Tetanus. — Determine how frequent the stimuli 
must be in order that the separate contractions 
may be fused into a smooth curve. 

Usually the muscle after contracting loses its 
irritability for several minutes. If this occur, 
the ring may be laid aside, covered with filter 
paper saturated with normal saline solution. 
Excellent curves are often obtained from muscle 
preserved in this way for half an hour or more. 



358 the outgo of energy 

The Work Done 
Influence of Load on Work done. — In the 

tracings obtained in the experiments on page 341 
with loads of 10 grams and upwards measure 
the distance from the summit of each curve to 
the abscissa. Calculate the gram-millimetres of 
work done at 10, 30, 50, 70, and 90 grams, 

using the formula W — — in which TV is work 

m 

done, in gram-millimetres ; iv, the weight lifted 

in grams, — i. e. the weight of the scale-pan and 

lever (about 12 grams) plus the weight put into 

the scale-pan (the weight of the muscle itself 

may be neglected) ; h, the height, in millimetres, 

to which the load is lifted ; m, the magnification 

of the lever. 

Write the results on the smoked paper. 

Note that within wide limits an increase in the 
load increases the work done by the muscle. 

Absolute Force of Muscle. — Secure the femur 
of a gastrocnemius muscle preparation in a mus- 
cle clamp and fasten the tendon to the rigid 
muscle lever. After-load the muscle until it 
just fails to lift the load when stimulated with 
tetanizing induction currents. 

The load which neither extends a contracting 
muscle nor allows it to shorten is a measure of 
the " absolute force " of the muscle. 



THE CHANGE IN FORM 



359 



Total Work done ; the Work Adder. — Attach 
a scale-pan to the cord that passes over the 
pulley on the axle of the 
work adder (Fig. 62). 

The Work Adder. 1 — A wheel 
of aluminium (Fig. 62) bears 
upon its axle a counterpoised 
muscle lever ending in a pawl 
through which the wheel is 
caused to revolve when the lever 
is pulled upward by the attached 
muscle. A second pawl pre- 
vents the wheel from turning 
back when the muscle relaxes. 
The axle of the aluminium wheel 
bears on the other side a pulley, 
from which the weight is sus- 
pended. The turning of the 
wheel winds the suspending cord 
upon the pulley and thus raises 
the weight. 




Fig. 62. The work ad- 
der ; about six-sevenths 
the original size. The han- 
dle is not shown. The 
muscle preparation is the 
double abductor suggested 
by Fick. 



Clamp the work adder to 

a stand in such a way that 

the scale-pan hangs free of the table. Fasten the 

tendon of the gastrocnemius muscle preparation 



1 Introduction to Physiology, 1901 
adder was devised by Fick. 



p. 225. The first work 



360 THE OUTGO OF ENEKGY 

to the lever of the work adder at a distance from 
the axis of the pulley equal to the radius of the 
pulley. Connect the muscle with the secondary 
coil of an inductorium arranged for single maxi- 
mal induction currents. Measure the distance of 
the pulley weight from the level of the axis of 
the pulley. Stimulate the muscle with induc- 
tion currents at intervals of one second until the 
fatigued muscle ceases to contract. (Stimulation 
may be made by opening and closing a simple 
key in the primary circuit in unison with the 
beat of a metronome.) 

Measure the height in millimetres to which 
the pulley weight has been lifted. Multiply this 
height by the weight. The product is the total 
work done in gram-millimetres. 

Total Work done estimated by Muscle Curve. — 
The total work done by the muscle may also be 
estimated by measuring in millimetres the height 
of each successive contraction recorded on the 
smoked paper, adding the several heights together, 
dividing the sum by the number of times the 
distance from the fulcrum of the recording lever 
to the point of attachment of the muscle is con- 
tained in the distance from the fulcrum to the 
writing point, and multiplying this quotient by 
the sum of the pulley weight plus the weight of 
the lever. 



THE CHANGE IN FORM 361 

In tetanus no weight is raised and no visible 
mechanical work is performed. That internal 
work is performed is shown by the rise in 
temperature. 

Time Relations of Developing Energy. — The 
simple muscle curve is a graphic record of the 
mechanical energy set free by the muscle in lift- 
ing a certain load. It is desirable to measure the 
maximum energy that the muscle can set free at 
each moment from the beginning of contraction 
to the point at which the greatest shortening is 
reached. 

Place the electromagnetic signal in the primary 
circuit of an inductorium arranged for maximal 
make induction currents. Arrange a tuning fork 
to write on a smoked drum beneath the line 
drawn by the writing point of the signal. Fasten 
the femur of a gastrocnemius muscle in the 
muscle clamp and attach the tendon to the heavy 
muscle lever. Place the three writing points in 
the same vertical line. Connect the binding posts 
on the muscle clamp and the lever with the posts 
of the secondary coil of the inductorium. " After- 
load " the muscle with 50 grams. Set the tuning 
fork vibrating. Spin the drum. Stimulate the 
muscle with a sinqle maximal make induction 
current. 

The muscle will not shorten until the energy 



362 THE OUTGO OF ENERGY 

set free is sufficient to lift a load of 50 grams. 
Turn the drum until the writing point of the 
signal rests in the line made by the signal when 
the muscle was stimulated. Let the drum be 
stationary. Set the tuning fork vibrating. Its 
writing point will mark a line synchronous with 
that drawn by the signal during the experiment. 
Eevolve the drum a little farther, until the 
writing point of the muscle lever reaches the 
point at which contraction began. Set the 
tuning fork vibrating again. Its writing point 
will mark a line synchronous with the beginning 
of contraction. The number of vibrations in the 
tuning fork curve between the two points just 
recorded is the interval between the stimulation 
of the muscle and the point at which the energy 
set free was sufficient to move a load of 50 
grams. Note this interval. 

After-load the muscle with 100, 150, 200, 250, 
and 300 grams, and repeat the above experiment 
after each addition of 50 grams. 

On coordinate paper set down as ordinates 
the several loads employed and along the abscissa 
the time intervals in hundredths of a second. 
Place a dot at the junction of the 50-gram line 
with the perpendicular cutting the abscissa at the 
figure indicating the interval observed between 
stimulation and the moment when the energy 



THE CHANGE IN FORM 363 

developed sufficed to raise the load. Eepeat this 
with other loads. Join the dots. The resulting 
line is a curve showing the absolute force of the 
muscle at successive intervals from the beginning 
to the end of the phase of rising energy. 

Eecord with this same muscle an isometric 
contraction (page 350). With the aid of the 
graduation scale of the isometric spring ascer- 
tain the maximum tension developed in the 
isometric contraction. Compare this result with 
that secured in the experiment just concluded 
on the time relations of developing energy. 

Elasticity and Extensibility 

Elasticity and Extensibility of a Metal Spring. — ■ 

Clamp the ergograph (Fig. 61) to the table in 
such a way that the writing point of the ergo- 
graph spring shall rest against a smoked drum. 
Attach a scale-pan to the spring near the free 
end. Turn the drum once round by hand, thus 
describing an abscissa on the smoked paper. 
With the forceps place 2 ten-gram weights very 
carefully on the scale-pan. 

The spring extends. Turn the drum 2 mm. 
and add another 20 grams to the scale-pan. 

A further extension of the spring will be 
recorded. 



364 THE OUTGO OF ENERGY 

Turn the drum 2 mm. again. Continue to 
record the extension of the spring after each 
addition of 20 grams until a load of 200 grams 
has been reached. 

It will be found that the extension curve is a 
straight line. The extension is directly propor- 
tional to the weights employed. 

Eemove the weights 20 grams at a time, turn- 
ing the drum 2 mm. after each lightening. 

The spring will return to its former length. 
Its elasticity (within the limits of extension here 
used) is perfect. 

Of a Rubber Band. — Place the muscle clamp 
in the stand of the heavy muscle lever (Fig. 60). 
Secure a rubber band in the jaws of the clamp 
and fasten the other end of the band to the 
muscle lever. Kepeat the preceding experi- 
ment, using 10-gram loads instead of 20-gram 
loads. 

The extension curve will again be a straight 
line. The return to the original length will not 
be complete. The elasticity of the rubber band 
is not perfect. An " extension remainder " is 
present. After a considerable time the exten- 
sion remainder will disappear and the band will 
return to its former length, provided the exten- 
sion was not too violent nor too long-continued. 

Of Skeletal Muscle. — Isolate in both limbs the 



THE CHANGE IN FOKM 365 

mass of long, parallel-fibred muscles extending 
along the inner side of the thigh from the pelvis 
to the tibia. Separate from the remainder of the 
pelvis the portion to which the muscles of both 
sides are attached. Remove the muscles of both 
sides together with the part of the tibia and the 
pelvis in which they are inserted. The muscles 
of the two sides thus form practically one long 
muscle held together in the middle by the small 
piece of bone into which they both are inserted 
(Fick's preparation, Fig. 60). 

Eepeat the preceding experiment, using this 
preparation in place of the rubber band. 

The extension curve is no longer a straight 
line, but approximately a parabola. In organic 
bodies, the increase in length is not proportional 
to the extending weights, but grows smaller as 
the weight increases. 

A perfectly fresh muscle weighted lightly (e. g. 
10 grams) usually returns to its original length 
when the extending weight is removed. With 
larger weights, the return is not at first com- 
plete : an extension remainder is observed, and 
the original length is reached only after a con- 
siderable time. 

Extensibility increased in Tetanus. — With the 
gastrocnemius muscle (unloaded except by the 
writing lever and scale-pan) draw an abscissa (1) 



366 THE OUTGO OF ENERGY 

with the muscle at rest ; (2) with the muscle 
tetanized. These abscissae record the length of 
the practically unloaded muscle in the resting 
and the active states. Place 10 grams in the 
scale-pan and again record the length of the 
muscle (1) at rest ; (2) tetanized. Make similar 
records for each 10 grams up to 100. 

It will be found that the extension curve falls 
more rapidly in the active than in the rest- 
ing muscle; the extensibility is increased in 
tetanus. 

Fatigue 

Skeletal Muscle of Frog. — 1. Let a gastro- 
cnemius muscle loaded with 10 grams write its 
contractions on a very slowly moving drum. 
Connect the secondary coil with the binding 
posts on the muscle clamp and the muscle lever. 
Stimulate the muscle once in two seconds with a 
maximal induction current, using make and break 
currents alternately. The correct interval may be 
obtained by listening to the beat of a metronome. 
Continue to record the contractions until the 
muscle will no longer shorten when stimulated 
(exhaustion). 

State the characteristic features of the fatigue 
curve. 

2. With a fresh muscle repeat the stimulation 



THE CHANGE IN FORM 367 

every two seconds until the height of contraction 
has diminished about one half. Now record the 
duration of the latent period, phase of rising 
energy, and phase of sinking energy (page 334) 
on a rapidly moving drum. 

Note the absolute and relative duration of 
these periods as compared with those of muscle 
not fatigued. 

3. Stimulate a sartorius from the same frog 
continuously with tetanizing currents and record 
the tetanus curve. 

State the differences between the fatigue curve 
thus secured and the curve obtained by less fre- 
quent stimulation. 

Attention has already been called to the dif- 
ferences which depend on the relative proportion 
of red and clear fibres (page 336). The latter 
are more easily fatigued. 

Human Skeletal Muscle. — 1. Arrange the ergo- 
graph to record the contractions of the abductor 
indicis, as directed on page 353. Place the point 
of the adjustable rod in the hole nearest the free 
end of the spring. 

Prepare also the large and small brass elec- 
trodes for artificial stimulation of the muscle and 
place them in position. 

Bring the writing point against a very slowly 
moving drum. Contract the muscle voluntarily 



368 THE OUTGO OF ENERGY 

twice every second, keeping time with the beat of 
a metronome, until two hundred contractions 
have been made. 

Now stimulate artificially every two sec- 
onds, using maximal make and break currents 
alternately, until two hundred contractions have 
been made. 

State the characteristics of the two fatigue 
curves, and compare the curves with those 
obtained from frog's skeletal muscle. 

2. From a fresh subject obtain a fatigue curve 
by artificial stimulation of the abductor indicis, 
using maximal make and break induction cur- 
rents alternately every two seconds, as directed 
in the preceding experiment. When the muscle 
has been stimulated two hundred times, contract 
it voluntarily every two seconds until two hun- 
dred contractions have been made. 

Compare the curves with those obtained in 
Experiment 1. 

Explain these paradoxes. 

It has been pointed out on page 357 that 
smooth muscle loses its irritability much more 
rapidly than striated muscle. 

Apparatus 

Normal saline. Bowl. Towel. Pipette. Glass plate. 
Volume tube. Bunsen burner. Inductorium. Two dry 



THE CHANGE IN FORM 369 

cells. Wires. Muscle clamp. Fine copper wire. One 
hundred ten-grarn weights. Muscle lever. Electro-mag- 
netic signal. Kymograph. Tuning fork. Cork clamp. 
Four needle electrodes. Pole-changer. Pin. Cork. Two 
stands with clamps. Ten one-gram weights. Muscle- 
warmer. Split shot. Ice. One per cent solution of 
veratrine acetate. Wheel-interrupter. Vibrating reed. 
Straw 36 cm. long with platinum contact. Mercury cup. 
Rigid muscle lever. Spring ergograph with rod. Hand 
clamp. Ergograph clamp. Large weight pan. Cotton. 
Two bent hooks. Heart-holder. Filter paper. Simple 
key. Work adder. Co-ordinate paper. Rubber band. 
Metronome. 



370 THE OUTGO OF ENERGY 



IV 



THE CENTRAL NERVOUS SYSTEM 
Simple Keflex Actions 

The Spinal Cord a Seat of Simple Reflexes. — ■ ■ 
1. By means of a hook or thread passed through 
the lower jaw suspend vertically a frog the brain 
of which has been destroyed with the seeker ; the 
legs must not touch the table. Pinch a toe with 
the forceps. 

The leg will be drawn up. 

A stimulus to the skin has caused the con- 
traction of muscles. The afferent impulse set 
going by the sensory stimulus is changed into 
a motor efferent impulse, This is an example of 
reflex action. 

2. Destroy the spinal cord with the seeker. 
Stimulate the skin of the right leg electrically 
and mechanically. 

In no case will the sensory stimulus call forth 
the reflex contraction of a skeletal muscle. Yet 
the nerves coming from the skin and going 



THE CENTRAL NERVOUS SYSTEM 371 

to the muscles are still intact. Only the spinal 
cord has been destroyed. 

The conversion of sensory into motor impulses 
for skeletal muscles is a function of the central 
nervous system. 

Influence of Afferent Impulses on Reflex Action. — 
Destroy the brain of a strong frog with the seeker. 
Gently pinch a toe of the right foot. 

Only the right leg will be drawn up. 

Pinch a toe of the left foot. 

Only the left foot will be drawn up. 

Pinch a finger. 

Only the corresponding arm will move. 

Pinch the whole foot sharply. 

More extended movements will be made. 

The character and location of the stimulus 
affect the resulting contraction. 

Threshold Value Lower in End Organ than in 
Nerve-Trunk. — 1. Carefully expose the sciatic 
nerve. Determine the least strength of tetanizing 
current that will cause a crossed reflex when 
applied to the skin of the foot. Now apply the 
same stimulus to the trunk of the nerve. 

As a rule, the intensity required to produce 
reflex action is less when the stimulus is applied 
to the peripheral endings of the sensory nerves 
than when the nerve-trunks are stimulated. 



372 THE OUTGO OF ENERGY 

2. Divide the skin over the back in the median 
line. Eaise the skin on one side until the small 
nerves which pass across the dorsal lymph sac to 
innervate the skin come into view. Sever from 
the surrounding skin a piece about one centi- 
metre square containing the endings of one of 
the nerves. Let the isolated piece with its nerve 
endings remain connected with the body only by 
the trunk of the nerve. As before, determine 
the least strength of tetanizing current that will 
cause a reflex movement when applied to the 
nerve-endings in the skin and to the nerve-trunk 
respectively. 

The threshold value for reflex action will again 
be found lower in the nerve-endings than in the 
nerve-trunk. 

Summation of Afferent Impulses. — Pass two 
fine copper wires about the frog's foot a centi- 
metre apart and connect them with the secondary 
coil. Connect the primary coil through a simple 
key with a dry cell. Stimulate with regularly 
repeated make induction currents of such strength 
that single stimuli cause no reflex contraction. 

Summation of the subminimal stimuli will 
finally cause reflex contraction. 

Determine that the number of stimuli neces- 
sary to produce a reflex becomes smaller when (1) 



THE CENTRAL NERVOUS SYSTEM 373 

the strength of the induction currents is increased, 
and (2) when the interval between the stimuli is 
lessened. 

Segmental Arrangement of Reflex Apparatus. — 
1. Gently pass the seeker over the abdominal 
walls on one side. 

The muscles in that region only will twitch. 

Eepeat the stimulus, but use a stronger 
pressure. 

The area contracting will increase in extent 
approximately in proportion to the increase in 
the stimulus. The afferent nerves from any one 
region are more closely related to the efferent 
nerves of that same region than to those of other 
regions. The fact that both afferent and efferent 
fibres spring from the cord at the same level 
suggests that their nerve cells lie also at approxi- 
mately the same level. On increasing the stim- 
ulus the afferent impulse spreads from segment 
to segment of the cord. Further evidence of the 
segmental arrangement will be gained by the 
following experiment. 

2. With a clean, sharp knife make transverse 
sections of the spinal cord, beginning in the cer- 
vical region. A short time after each section 
test the reflexes from the hind limb by mechani- 
cal stimulation. 



374 THE OUTGO OF ENERGY 

Note the level below which no section can be 
made without rendering the reflex impossible. 
The nerve cells concerned in this reflex lie on 
the caudal side of this line. 

Now in a second frog make transverse sections, 
beginning at the caudal end of the cord, and test 
the reflexes as before, until the level is reached 
beyond which a section will destroy the reflex. 

Observe that the portion of the cord comprised 
between the two levels determined forms a seg- 
ment which contains the central apparatus con- 
cerned in the reflex studied. 

Reflexes in Man. — 1. From the Shin. — Eub 
the plantar surface of the foot gently with some 
hard object. 

The foot will be retracted reflexly. 

Similar results may be obtained by rubbing 
the skin of the inside of the thigh, which will 
cause contraction of the cremaster muscles ; or by 
rubbing the skin of the abdomen, which will be 
followed by contraction of the abdominal muscles. 

These reflexes are of importance in clinical 
diagnosis because by means of them the seat of a 
diseased area in the central nervous system may 
sometimes be defined, since the reflex depends on 
the integrity of the corresponding reflex arc. 

2. Cornea Reflex. — Touch the cornea gently 
with a thread. 



THE CENTRAL NERVOUS SYSTEM 375 

The eye will be closed involuntarily. 

3. Throat Reflex. — Touch the posterior wall 
of the throat. 

The movements of swallowing will usually 
follow. 

4. Pupil Reflexes ; Light Reflex. — Close one 
eye for several seconds, then open it quickly. 

Note the contraction of the pupil. 

5. Consensual Reflex. — Close one eye as before, 
but watch the pupil of the other eye when the 
first is opened again. 

The pupil will contract. 

6. Accommodation Reflexes. — Look alternately 
at a near and a far object. The pupil will con- 
tract when the eye adjusts itself to see the near 
object. 

Tendon Eeflexes 

Knee Jerk. — Sit in such a position that the 
knee is bent at a right angle, and the foot hangs 
free. Let an assistant strike the patellar liga- 
ment with the side of the hand. 

Note the sudden contraction of the extensors 
of the thigh, the so-called knee jerk. 

Flex the knee at different angles and deter- 
mine in which position the resulting contraction 
is greatest. 

Knee jerk can be obtained only within certain 
limits of extension. 



376 THE OUTGO OF ENERGY 

Let the subject immediately before the stimu- 
lus is applied forcibly contract some other group 
of muscles ; clench the hand, for example. 

The knee jerk is reinforced. 

Ankle Jerk. — Bend the foot at right angles to 
the leg, and strike the tendo Achillis. The ex- 
perimenter should hold the end of the foot in his 
left hand. 

Contraction of the gastrocnemius muscle will 
be observed. 

Gower's Experiment. — Strike the side of the 
tendo Achillis. 

A contraction will result. 

Support the other side of the tendon so that 
the gastrocnemius muscle will not be stretched 
by the blow. Eepeat the experiment. 

No contraction follows. The tendon jerk re- 
quires for its production a rapid stretching of the 
muscles involved in the contraction. 

Try to obtain tendon jerks from other muscles ; 
for example, the triceps humeri, flexors of hand, 
and masseter muscles. 

Normally no response will be obtained. 

The experiments are of value in diagnosis of 
diseases of the central nervous system. 



the centeal nekvous system 377 

Effect of Strychnine on Keflex Action 

Inject with a glass pipette a few drops of 0.5 
per cent solution of sulphate of strychnine into 
the dorsal lymph sac of a frog the brain of which 
has been destroyed with a seeker. 

After a few minutes, very weak afferent 
impulses will be sufficient to call forth general 
spasmodic reflex actions. Note that (1) the 
strychnine reflexes are paroxysmal, (2) the mus- 
cles fall into more or less prolonged rigidity (teta- 
nus), and (3) the extensors overcome the flexors, 
the limbs being strongly extended. 

The characteristic action of strychnine is evi- 
dently not dependent on the brain. 

Destroy the spinal cord with a seeker. 

Stimulation of muscles and nerves will not 
cause spasmodic contractions. 

Strychnine acts on the spinal cord, but not on 
the muscles or the peripheral nerves. 

Complex Co-ordinated Eeflexes 

Removal of Cerebral Hemispheres. — Place a 
frog under a glass jar containing a small sponge 
wet with ether. Be very careful not to kill the 
frog. When insensibility is complete, place the 
animal on a frog-board. Cut through the skin in 
the median line of the skull, from the nose to the 



378 THE OUTGO OF ENERGY 

vertebral column. Connect the front margins of 
the two tympanic membranes by a transverse in- 
cision through the skin. This transverse line 
will pass over the junction of the cerebral lobes 
with the optic lobes. Strip off the parietal bones 
with forceps, beginning at the anterior end oppo- 
site the anterior margin of the orbit. When the 
cerebral hemispheres are uncovered, they may be 
removed from before backwards. Avoid injuring 
the optic lobes. Work rapidly but carefully. If 
the ether effect diminish before the operation be 
finished, replace the frog under the glass jar for 
a few moments. As soon as the hemispheres are 
removed, sew up the wounds in the skin. 

Note the signs of profound inhibition. 

If the operation be done carefully, the shock 
will gradually pass away, and the functions possi- 
ble in the absence of the cerebrum may then be 
determined. Put the frog aside, moistening his 
skin occasionally, but not otherwise disturbing 
him, and prepare a second frog for the experi- 
ment upon the " croak reflex " (page 379). When 
this operation is completed, resume the observa- 
tions on the first frog, while the second frog re- 
covers from the shock. 

1. Posture, etc. — Write down the differences 
between the frog from which only the cerebral 
hemispheres have been removed and a frog in 



THE CENTRAL NERVOUS SYSTEM 379 

which the whole brain has been destroyed with 
the seeker, in respect to posture, power to regain 
feet when laid on back, respiratory movements, 
position of eyelids, leaping and swimming. 

2. Balancing Experiment. — Place the frog on a 
somewhat roughened board, about 20 inches long, 
8 inches wide, and 1 inch thick. Tilt the 
board gradually. 

The frog remains motionless until his centre 
of gravity is disturbed. He then moves forward 
in an attempt to reach a stable position. By 
careful management, he can be made to climb up 
the inclined board, perch upon the narrow edge, 
and, the board still turning, descend head-first on 
the opposite side. 

3. Retinal Reflex. — Place the frog deprived of 
cerebral hemispheres in front of a bright light ; 
for example, an incandescent electric lamp. In- 
terpose some object, such as a small instrument 
case, between the light and the frog, so that a 
strong shadow is cast upon the frog's eyes. 
Stimulate the frog by pinching the skin of the 
back. 

The frog will jump, but will avoid the object 
which casts the shadow. 

4. Croak Reflex. — Sever the large hemispheres 
from the remainder of the brain of another frog 
by passing a knife through the cranium to the 



380 THE OUTGO OF ENERGY 

base of the skull from side to side in a line join- 
ing the anterior margins of the tympanic mem- 
branes. (Where possible, a male frog should be 
selected for this experiment. Males may be rec- 
ognized by the cushion-like thickening on the 
innermost digit of the manus, or hand ; the male 
Eana esculenta possesses bladder-like, resonating 
pouches connected on each side with the mouth 
cavity.) After the immediate shock of the opera- 
tion has passed, stroke the back over the anterior 
half of the spinal cord. 

Reflex croaking will be observed. 

The croak reflex can be inhibited by simultane- 
ous pinching of one of the limbs or other strong 
stimulation. (Compare page 384.) 

If the experiments on the frog in which the 
cerebral hemispheres were extirpated were not 
satisfactory, repeat them on this frog in which 
the hemispheres were simply separated from the 
remainder of the brain. 

These observations teach that very complicated 
co-ordinated actions are possible in the absence 
of the large hemispheres. Only simple reflexes 
are possible when the whole brain is removed. 
Consequently, the seat of these complicated re- 
flexes must lie in the brain between the cord and 
the cerebral hemispheres. 



the central nervous system 381 

Apparent Purpose in Eeflex Action 

1. Destroy the brain of a frog with the seeker. 
Dip small pieces of filter paper in strong acetic 
acid. Eemove the superfluous acid, lay the 
paper bearing the acid on (1) the frog's thigh, 
(2) the foot, (3) the back. After each stimulation 
note the character of the reflex movement, and 
then carefully wash the acid from the skin. 

The movements are related to the areas stimu- 
lated in a certain purposeful way. Efforts are 
made apparently to brush away the acid paper. 

2. Place the acid on the flank of the right leg. 
Usually the leg stimulated strives to brush away 
the paper. Hold this leg fast. 

The other leg (the left) will be used to re- 
move the acid from the opposite limb. (This 
experiment succeeds best in strong, lively frogs.) 

3. Place an uninjured frog in an evaporating 
basin containing sufficient water to immerse the 
frog to the neck and covered with wire gauze 
to keep him from jumping out. Warm the 
water. 

As the temperature rises to from 20°-30° C. 
the frog will attempt to escape. 

Eepeat the experiment with the frog the brain 
of which has been destroyed. 

No movements of escape will be noticed. 



382 THE OUTGO OF ENERGY 

About 35°, muscular twitchings will be seen. 
At 38°-40° death takes place and the muscles 
become rigid (heat rigor). 

This observation shows that volition in all 
probability is absent in the brainless frog. It 
follows that reflex actions are not volitional; 
their " purpose " is only apparent. 

Eeelex and Ee action Time 

Reflex Time. — Destroy the brain of a frog with 
the seeker. Hold one leg of the frog aside with 
the glass rod. Bring beneath the other a small 
beaker almost full of dilute sulphuric acid 
(2:1000). Eaise the beaker until the foot is 
immersed to the ankle. Count the seconds be- 
tween the application of the stimulus (sulphuric 
acid) and the withdrawal of the foot. 

This interval is the reflex time. 

Wash the foot carefully in the bowl of water. 

Reaction Time. — Smoke a drum. Eaise the 
drum off its friction bearing by turning the screw 
at the top of the shaft. Place the writing point 
of an electromagnetic sigual against the smoked 
paper. Arrange a tuning fork to write its curve 
near that of the signal. Connect the signal 
through two simple keys and a dry cell with the 
primary coil of an inductorium arranged for 
maximal single induction currents (posts 1 and 



THE CENTEAL NERVOUS SYSTEM 383 

2). Let stimulating electrodes pass from the 
secondary coil (bridge up) to the tongue of the 
subject. Let the subject hold one key closed un- 
til he feels the stimulus on the tongue. 

Direct the subject to shut his eyes. Let the ob- 
server start the tuning fork, spin the drum, and 
stimulate the subject by completing the primary 
circuit. The instant the subject perceives the 
stimulus, he will break the circuit by releasing 
his key. By means of the tuning fork curve 
determine the interval between stimulation and 
response. This interval is the reaction time plus 
the errors of observation ; for example, the latent 
period of the electromagnetic signal. Eepeat the 
experiment three times and take the mean of the 
results. 

In the laboratory note-book make a list of the 
links in the chain between stimulus and re- 
sponse, and state as far as possible the errors of 
observation. 

Reaction Time with Choice. — Connect the 
side cups of a pole-changer (without cross wires) 
to the posts of the secondary coil. Connect one 
pair of end cups with the usual stimulating elec- 
trodes, the other pair with large brass electrodes 
covered with wet cotton. Let the ordinary elec- 
trodes touch the forehead, the other pair the hand 
of the subject. The other connections should re- 



384 THE OUTGO OF ENERGY 

main as before. Eepeat the preceding experi- 
ment but tell the subject to signal only when 
the tongue (or hand) is stimulated. In order to 
do this he must add to his former reaction a de- 
cision as to the part stimulated. 

Eeaction time with choice is longer than sim- 
ple reaction time. In general, the more compli- 
cated the mental processes involved, the longer 
will be the reaction time. 

Inhibition of Eeflexes 

Through Peripheral Afferent Nerves. — Expose 
the left sciatic nerve for a distance of about 15 
mm. in a frog the brain of which has been de- 
stroyed. Tie a thread around the distal end, and 
sever the nerve at the peripheral side of the liga- 
ture. Place the central stump of the nerve on 
the electrodes of the inductorium, the short-cir- 
cuiting key being closed. Make the primary 
circuit, and set the hammer vibrating. Now open 
the short-circuiting key, bring the right foot of 
the frog into the dilute sulphuric acid up to the 
ankle, and count the seconds from the moment 
of immersion to the moment of withdrawal, con- 
tinuing meanwhile the stimulation of the central 
end of the left sciatic nerve. 

The latent period will be much prolonged. 

Wash off the acid carefully. 



THE CENTRAL NERVOUS SYSTEM 385 

Keflex actions may be inhibited by the simul- 
taneous stimulation of sensory nerves. 

Through Central Afferent Paths ; the Optic 
Lobes. — 1. Expose the brain according to the 
directions already given (page 377). Immediately 
posterior to the cerebral hemispheres lie the optic 
lobes, two gray spherical bodies. Separate the 
cerebral hemispheres from the optic lobes by a 
transverse incision, and carefully remove the 
hemispheres. Wait until the shock of the opera- 
tion has passed. Now suspend the frog so that 
the tips of the toes hang above a shallow dish 
containing water made strongly sour to the taste 
with dilute sulphuric acid. Determine the reflex 
time. Wash off the acid and, after a moment's 
rest, sprinkle a very little finely powdered com- 
mon salt on the cut surface of the optic lobes. 
Again determine the reflex time. 

The reflex time will be found to be markedly 
increased by the stimulation of the optic lobes. 

2. Prepare a second frog in the same manner. 
Determine the reflex time. Now instead of stim- 
ulating the optic lobes, remove them, and again 
determine the reflex time. 

The removal of the optic lobes shortens the 
reflex time. 

30 



386 the outgo of enekgy 

The Roots of Spinal Nerves 
Destroy the brain of a strong, large frog with 
a seeker. Divide the skin over the vertebral 
column from the upper end of the urostyle to 
the level of the fore limbs. Hook back the 
flaps of skin. Remove the longitudinal muscles 
on either side of the spines of the vertebrae, thus 
exposing the bony arches. Saw through the 
arches of the 8th, 7th, and 6th vertebrae (there 
are ten vertebrae in the frog, counting the uro- 
style) in the order named. Clear away the bone 
and the underlying tissues until the last three or 
four pairs of roots shall be plainly seen. Grasp 
the fllum terminale and cautiously lift the cord 
until the spinal nerve roots are clearly displayed. 
The anterior roots are hidden by the large, 
superficial posterior roots. The conspicuous pos- 
terior root which seems to be the last is, in real- 
ity, the 9th, the next to the last ; the last, or 
10th, is smaller and lies close to the fllum termi- 
nale. Place a silk ligature about the middle 
of an anterior and a posterior root on the right 
side. "With single induction currents as stimuli 
observe that (1) the stimulation of only the cen- 
tral end of the posterior root calls forth a (re- 
flex) movement, and (2) the stimulation of only 
the peripheral segment of the anterior root causes 
movement. 



THE CENTRAL NERVOUS SYSTEM 387 

On this same side cut all the posterior roots. 

No stimulus applied to the right leg will now 
discharge a reflex action. But stimuli applied to 
sensory nerves elsewhere may still cause reflex 
movements of the right leg. Motor impulses still 
pass to these muscles. But only the anterior 
roots remain. 

Hence the anterior roots of spinal nerves trans- 
mit motor impulses from the spinal cord towards 
the muscles (efferent impulses) ; the posterior 
roots transmit sensory impulses from sensory sur- 
faces towards the spinal cord (afferent impulses.) 

Ludwig's Demonstration. — Destroy the brain 
of a large frog with the seeker. Remove the 
thoracic and abdominal viscera, taking care not 
to injure the sciatic nerve plexus. Eemove the 
7th and 8th vertebras, taking the greatest pains 
not to injure the nerve roots. Divide the body 
transversely at this level, so that the anterior 
and posterior halves shall remain connected only 
by the anterior and posterior sciatic roots. Keep 
the roots moist with normal saline solution. 

Demonstrate again that the anterior roots 
transmit efferent, and the posterior roots afferent 
impulses. 

Localization of Movements at Different Levels of 
the Spinal Cord. — Separate the three roots which 
form the sciatic nerve. After tying a thread 



388 THE OUTGO OF ENERGY 

about each root sever it from the spinal cord by 
a cut on the proximal side of the thread. Stimu- 
late each nerve with a very weak tetanizing cur- 
rent. Note the different results obtained from 
nerves arising at different levels of the cord. 
Stimulation of the most anterior root causes 
marked flexion of the limb ; stimulation of the 
middle roots, extension and internal rotation; 
and of the most posterior, simple extension. 

In a frog whose nerves have not been cut 
expose the spinal cord and stimulate it at differ- 
ent levels in both directions along its length. 
The various movements of the hind limbs are 
localized at different levels of the cord. 

Distribution of Sensory Spinal Nerves 

Destroy the brain of a large frog with the 
seeker. Expose the lower half of the spinal cord 
by the method already described. On one side 
cut the dorsal sensory root of the 8th spinal nerve 
and on the other cut the sensory root of the 7th, 
9th, and 10th. After the section of each root 
test the cutaneous sensibility of the limbs by 
placing upon the skin small pieces of filter paper 
(two mm. square) moistened, not dripping, with 
0.2 per cent sulphuric acid. Make a map of the 
anaesthetic areas in each leg, and note the lack 
of correspondence. 



THE CENTRAL NERVOUS SYSTEM 389 

Many skin areas are supplied by fibres from at 
least two sensory roots. The fields of distribution 
overlap. 

Muscular Tonus 

Brondgeest's Experiment. — Fasten a lightly 
etherized frog back uppermost on the frog-board. 

In a line between the ilium and the coccyx 
open the pelvic cavity by cautiously dividing the 
skin, fascia, and muscle. Divide the sciatic nerve 
roots on the operated side. Pass a hook or thread 
through the jaw and hang the frog up. 

Observe that the limb the nerves of which 
have been cut is relaxed, so that the toes hang 
lower than those of the limb which still retains 
its connection with the central nervous system. 

Apparatus 

Normal saline. Bowl. Towel. Pipette. Stand. 
Muscle clamp. Bent hook. Inductorium. Dry cell. 
Electrodes. Large brass electrodes. Cotton. Key. 
Frog-board. Fine copper wire. One-half per cent solu- 
tion of strychnine sulphate. Glass jar with ether and 
sponge. Balancing board. Strong acetic acid. Filter 
paper. Evaporating basin. Wire gauze. Bunsen burner. 
Thermometer. Dilute sulphuric acid (0.2 per cent). 
Beaker. Kymograph. Electro-magnetic signal. Tuning- 
fork. Pole-changer. Vertebral saw. 



390 THE OUTGO OF ENERGY 



V 

THE SKIN 
Sensations of Temperature 

Hot and Cold Spots. — With, a lead-pencil point 
carefully explore an area about an inch square 
on the back of the wrist or hand. Mark with 
black ink the places where a distinct sensation of 
cold is felt, and with red ink those where the 
sensation is one of warmth. 

The places indicated are the so-called hot and 
cold spots. 

Outline. — Attempt to define more exactly the 
outline of one of the cold spots. 

The spots are of irregular shape, — blotches 
rather than points. 

Mechanical Stimulation. — 1. Gently tap one 
end of a small wooden rod the other end of which 
is placed on a well-defined cold spot. 

The mechanical stimulation of the cold spot 
will give a sensation of cold. 

2. Stimulate a warm spot mechanically. 

Chemical Stimulation. — Eub a menthol pencil 
over a small area on the back of the hand. 



THE SKIN 391 

A sensation of cold will be perceived. This is 
due to chemical irritation of the cold spots. The 
temperature of the area does not fall. 

Electrical Stimulation. — It has been found that 
the stimulation of a well-defined cold or warm 
spot with moderately strong induced currents 
causes a sensation of cold or warmth respectively. 

Temperature After-Sensation. — Stimulate a cold 
spot mechanically with a pencil point. Eemove 
the point. 

The sensation of cold outlasts the stimulus. 

Balance between Loss and Gain of Heat. — Pro- 
vide three beakers of water. Heat them to 20°, 
30°, and 40° C, respectively. Place a finger of 
one hand in the water at 20°, and a finger of the 
other hand in the water at 40°. After the re- 
spective sensations of cold and warmth have 
disappeared, place both the fingers in the water 
at 30°. 

The finger from the cold water will seem warm 
and that from the warm water cold. The tem- 
perature of the skin equals the balance between 
its heat loss and heat gain. When this tempera- 
ture is raised or lowered, the warm spots or cold 
spots respectively are stimulated. 

Fatigue. — Provide three beakers containing 
water at 10°, 32°, and 45° 0. respectively. Place 
a finger of one hand in the beaker at 32°, and a 



392 THE OUTGO OF ENERGY 

finger of the other hand in the beaker at 45°. 
After 45 seconds place both fingers in the water 
at 10°. 

The finger taken from the water at 3.2° (which 
is about the normal temperature of the hand) will 
feel colder than the other finger. Extreme tem- 
peratures of heat or cold fatigue the temperature 
spots. 

Relation of Stimulated Area to Sensation. — In- 
sert a finger of one hand in a beaker of warm or 
cold water. Note the sensation. Insert a finger 
of the other hand in the water. 

The intensity of the sensation will increase 
with the extent of the surface stimulated. 

Perception of Difference. — Provide two beakers 
of water, one at 30°, the other slightly warmer or 
colder. By introducing a finger first into the one 
and then into the other, and varying the tem- 
perature of the water, ascertain how small a 
difference in temperature can be detected. 

Usually a difference of 0.5° C. is easily recog- 
nized. 

Relatively Insensitive Regions. — 1. Compare 
the temperature sensation perceived on touching 
with a pencil point the median line of the fore- 
head, nose, and chin with that perceived on 
touching the skin on either side of the median 
line. 



THE SKIN 393 

The skin in the median line of the body is 
comparatively insensitive to temperature varia- 
tions. 

2. Similarly compare the mucous membrane 
with the skin. 

The mucous membranes are much less sensitive 
than the skin. 

Sensations of Pressure 

Pressure Spots. — Explore the surface of the 
forearm by bringing the blunted point of a needle 
gently in touch with the skin. 

At certain spots a distinct sensation of contact 
will be perceived. Other spots will give only 
dull sensations. Pressure, like heat and cold, is 
appreciated by scattered sense-organs in the skin, 
not by diffuse general sensation. 

Note the relation of the pressure points (1) to 
the hair follicles, and (2) to the warm and cold 
spots mapped out in previous experiments. 

Threshold Value. — Take from the human head 
several straight, strong hairs. Cement each to 
the end of a little stick of soft pine to serve as 
a handle. Provide a special lever, made as fol- 
lows : With a hot pin burn a small hole at the 
middle of a straw about 25 cm. in length. Pass a 
needle through this hole into a cork held in the 
muscle clamp. Press the free end of the hairs 



394 THE OUTGO OF ENERGY 

against different parts of the skin of the hand, 
arm, and face. Select hairs which when pressed 
against the skin of the respective regions give no 
sensation of pressure. Shorten the hairs until 
the pressure is just perceptible. This will be the 
" pressure threshold." Make a loop in a short 
silk thread and pass the loop about the lever 
exactly one millimetre from the axis. Hang on 
the end of the thread a light bent hook. Coun- 
terpoise the lever very exactly, so that the 
slightest force applied to the end of the straw 
will raise the lever from the after-loading screw. 
By counterpoising in this way, the lever becomes 
a balance. On the bent hook hang a ring of 
German silver wire weighing one decigram (0.1 
gram). Find a point on the lever 100 mm. from 
the axis. The weight of one decigram suspended 
1 mm. from the axis of the lever will be raised 
by a force of -^fo of a decigram, equal to one 
milligram (0.001 gram) applied 100 mm. from 
the axis. At 50 mm. from the axis, 0.1 gram, 
suspended 1 mm. from the axis, will be lifted by 
a force of -g-±o gram (0.002 gram). Find the dis- 
tance from the axis at which each testing-hair, 
when pressed vertically against the lever, will 
just fail to lift the lever; in other words, the 
point at which the pressure will be just sufficient 
to bend the hair. The number of millimetres 



THE SKIN • 395 

between this point and the axis of the lever, 
multiplied by one-tenth, will give the bending 
pressure of the hair in the fraction of a gram. 
Make ten observations on each hair and mark the 
mean bending value on the wooden handle. 

Touch Discrimination. — 1. Close the eyes and 
let an assistant test the different parts of the 
skin of the hand, arm, and face for discrimina- 
ting power. For each test separate the points of 
the aesthesiometer until they can be felt as two 
(ordinary drawing dividers or compasses can be 
used for an sesthesiometer). 

Eecord your results in millimetres for finger- 
tips, palm of hand, back of fingers, back of hand, 
back of wrist, flexor and extensor surfaces of fore- 
arm, forehead, cheeks, lips, and tongue. 

2. Separate the points of the sesthesiometer 
about 20 mm., and draw them gently side by 
side along the extensor surface of the forearm 
from the elbow to the wrist. Kepeat the experi- 
ment on the flexor surface. Try the same for 
the cheek and lips, beginning near the ear and 
drawing the points so that one shall go above 
and the other below the mouth. 

Describe -the sensation in each case, and sug- 
gest an explanation. 

Weber's Law. - — Place the hand palm upward 
in a comfortable position on the table, (.'lose 



396 THE OUTGO OF ENERGY 

the eyes. Let an assistant place on the last 
phalanx of the middle and index fingers a small 
round box containing ten small shot. 

When the subject has formed a clear percep- 
tion of the weight, let an assistant add or 
subtract shot, and record the number of shot cor- 
responding to the smallest difference in weight 
perceived by the subject (whose eyes of course 
should be kept closed). Kepeat the experiment 
with 20, 30, 40, and 50 shot in the box respec- 
tively. Determine in each instance the ratio of 
the number of shot added or subtracted to the 
number with which each experiment was begun. 

This ratio will be approximately constant. 
The degree of stimulation necessary to cause the 
perception of difference always bears the same 
ratio to the degree of stimulation already applied. 
Weber's law is less true for very small and very 
large weights than for those of medium value. 
It is a general law and holds good for visual 
judgments, etc. 

After-Sensation of Pressure. — Place a rubber 
band about the head and allow it to remain for 
several minutes. 

On removing the band, a distinct after-sensa- 
tion of pressure will be felt. 

Temperature and Pressure. — Place on the back 
of the hand supported on the table a coin the 



THE SKIN 397 

temperature of which has been made such that 
it feels neither warm nor cold. Compare the 
pressure sensation (apparent weight) of this "nor- 
mal" coin with that of similar coins warmed 
and cooled. 

The hot or cold coin will seem heavier than 
the " normal " coin of equal weight. 

Touch Illusion ; Aristotle's Experiment. — Cross 
the right middle finger over the right index finger 
and place them on the palm of the left hand. 
Place a small shot between the crossed fingers in 
such a way that it shall touch the ulnar side of 
the middle finger and the radial side of the index 
finger. Eoll the shot in the palm of the hand. 

A sensation of two objects will be felt. 

Apparatus 

Black and red ink. Small wooden rod. Menthol pen- 
cil. Inductorium. Dry cell. Electrodes. Key. Three 
beakers. Stand. Ring. Wire gauze. Bunsen burner. 
Thermometer. Needle with blunted point. Muscle lever. 
Gram and ten-gram weights. German silver ring weigh- 
ing 0.1 gram. Silk thread. Four small wooden handles 
for pressure-hairs. Bent hook. Drawing dividers (as 
sesthesiometer). Small round box containing at least 50 
shot. Rubber band large enough to go around the head. 



398 THE OUTGO OF ENERGY 

VI 

GENERAL SENSATIONS 
Tickle 

Irradiation. — Gently touch the skin near one 
nostril with a dry camel' s-hair brush. 

Note (1) the strong sensation produced by 
the slight stimulus ; (2) the irradiation beyond 
the spot stimulated. 

After image. — Repeat the stimulus of the pre- 
ceding experiment. 

Measure in seconds the time during which 
the sensation outlasts the stimulus (after image). 

Topography. — Test the tickle sensation at vari- 
ous points on the skin of the face, hands, and 
forearms. Determine whether the sensation is 
greatest about the several openings, where skin 
joins mucous or serous membranes; e.g., the 
nostrils, the conjunctival sac, the auditory canal. 
Do the results indicate a protective mechanism ? 

Summation. — In one of the sensitive areas 
found in the preceding experiment determine the 
difference between the response to a single stim- 
ulus and to successive stimuli. 

Fatigue. — In any sensitive area determine (1) 
the quickness with which the apparatus for the 
sensation of tickle is fatigued ; (2) the duration 
of fatigue. 



general sensations 399 

Pain 

Threshold Value. — Arrange an inductorium for 
tetanizing currents. Place the electrodes on 
the tip of the tongue, and move the secondary 
toward the primary coil until no farther move- 
ment can be made without causing the stimula- 
tion to become painful. Determine for this 
region and for others of the mucous membrane 
of the mouth and of the skin what distance of 
the secondary coil from the primary separates the 
stimulus at which pain is just perceived from 
that at which the pain is distinct. 

Latent Period. — In several individuals measure 
approximately the interval between the applica- 
tion of the stimulus (single break shock) and the 
resulting painful sensation. 

Summation. — Determine the number of sub- 
minimal stimuli necessary to produce pain. 

Topography. — Map upon the skin of the face 
and arm the areas specially sensitive to pain. 

Individual Variation. — Compare the reactions 
of several individuals, and note the differences in 
threshold value, latent period, summation, and 
topography. 

Temperature Stimuli. — Fill two bowls or large 
beakers with water twenty-five degrees respec- 
tively, hotter and colder, than the temperature 



400 THE OUTGO OF ENERGY 

of the hand. Determine whether the increase 
or the corresponding decrease in temperature is 
the more painful to the immersed hand. 

Motor Sensations 

Judgment of Weight. — Lift the same weight 
twice, at first very slowly and then quickly. 

The weight will appear lighter when raised 
quickly. 

Sensation of Effort. — " Hold the finger as if to 
pull the trigger of a pistol. Think vigorously 
of bending the finger, but do not bend it. 

" An unmistakable feeling of effort results. 

" Repeat the experiment, and notice that the 
breath is involuntarily held, and that there are 
tensions in other muscles than those that would 
move the finger/' (Sanford.) 

Sensation of Motion. — Let the forearm and 
hand rest upon a table. Bring the four fingers 
of the hand together, and turn the hand so that 
it shall rest upright upon the ulnar side of the 
little finger. Close the eyes. Abduct the first 
finger. 

The second, third, and fourth finger will seem 
to move in a direction opposite to the movement 
of the first. 



TASTE 401 

VII 

TASTE 

Threshold Value. — Prepare solutions of cane 
sugar of the following strengths : 1 : 1000, 1 : 800, 
1 : 600, 1 : 400, 1 : 200, 1 : 100. Take half a 
teaspoonful of the weakest solution into the 
mouth, roll it upon the tongue, and swallow 
it. Note whether a sweet taste can be per- 
ceived. Rinse the mouth thoroughly. Proceed 
with solutions of increasing strength until the 
sweet taste is just perceptible. 

Topography. — 1. Select a solution of sugar 
slightly more concentrated than that just per- 
ceived to be sweet. With a small camel's-hair 
brush apply this solution to the several parts 
of the tongue and the palate. Determine the 
regions sensitive to taste. The. mouth must be 
rinsed frequently. 2. Dry the upper surface of 
the tongue with a handkerchief. With a finely 
pointed camel's-hair brush apply a twenty per 
cent sugar solution to the individual fungiform 
papillae and to the mucous membrane between 
them. Determine whether only the papilke 
perceive taste. 

Relation of Taste to Area stimulated. — Swallow 
a very small quantity of a minimal solution of 
sugar, as determined in the experiment upon 



402 THE OUTGO OF ENERGY 

threshold value. Einse the mouth, and then 
swallow a much larger portion of the solution. 

The taste will be perceived more strongly, the 
larger the area stimulated. 

Electrical Stimulation. — 1. Connect two small 
zinc electrodes through a simple key to a battery 
of four dry cells. Apply one electrode to an in- 
different region, the other to the tongue. Close 
the key. 

Note the sour taste at the positive pole and 
the alkaline taste at the negative. 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 403 



VIII 

INTRODUCTION TO PHYSIOLOGICAL 
OPTICS 

All visible objects give out light, either of their 
own making, like the sun, or that which conies 
from some external source and falls upon their 
surfaces. Eays that fall upon any surface may 
disappear (absorption), or be thrown back from 
the surface (reflection), or, if the body be trans- 
parent, pass into it, in which case they are often 
bent from their course (refraction). 

Eeflection from Plane Mirrors 

Angles of Incidence and Reflection. — Place in 
front of the condenser in the lantern (Fig. 63) 
the diaphragm with 2 mm. aperture. Cover the 
round window in the optical box with the plain 
glass slide. Remove the cork from the tin cylin- 
der. Put a piece of lighted Japanese incense in 



404 



THE OUTGO OF ENERGY 




INTRODUCTION TO PHYSIOLOGICAL OPTICS 405 

the hole in the cork. Put back the cork. Place 
the incense-holder in the optical box and put the 
glass lid on the box. Arrange the lantern to 
throw a beam of light through the window into 
the box. The smoke will be made luminous by 
the light so that the path of the rays can be seen. 
Make the rays parallel by pushing in the draw- 
tube holding the outer projecting lens of the 
lantern. Set the plane mirror against the side 
of the box. Let the rays fall obliquely upon 
the mirror. Accurate measurement would show 
(1) that the incident ray, the reflected ray, and 
the perpendicular to the point of incidence, all 
lie in the same plane, and (2) that the angle 
between the incident ray and the perpendicular 

— angle of incidence — is equal to the angle 
between the perpendicular and the reflected ray 

— angle of reflection (Hero of Alexandria, about 
100 B.C.). 

Reflection from Concave Mirrors 

Principal Focus. — 1. Place the concave mirror 
(the polished inner surface of the segment of a 
sphere of 5 cm. radius) at right angles to the 
pencil of parallel rays. 

The rays will be reflected to a point 2.] cm. 
from the mirror. 1 This point, to which parallel 

1 Much smoke will make the rays less visible. The incident 



406 THE OUTGO OF ENERGY 

rays are converged, is the principal focus of the 
concave mirror. The distance between the prin- 
cipal focus and the reflecting surface is termed 
the principal focal distance ; it is one half the 
radius of curvature. Accurate measurement 
would show that the angle between the incident 
ray and the perpendicular, 1 in this ease the radius 
of the spherical surface, equals the angle of 
reflection. 

2. Take the mirror from the box and set it 
in the principal axis of the beam coming from 
the lantern. Replace the 2 mm. diaphragm by 
the diaphragm with L-shaped aperture. At the 
principal focus of the concave mirror hold the 
small round screen with slender handle. 

The inner rays of the beam will be inter- 
cepted by the screen. The outer rays will be 
reflected from the mirror and an inverted, real 
image of the L-shaped aperture will be seen upon 
the screen. The image will be smaller than the 
object. When the distance between the mirror 
and the object is less than the radius of curvature 
but greater than the focal distance, the image 
is real, inverted, and larger. With concave 
mirrors, real images are always inverted. 

and the reflected beam may be compared by turning the mirror 
slightly, so that they lie side by side. 

1 It is assumed that the spherical surface is composed of an 
infinite number of plane surfaces. 



INTRODUCTION" TO PHYSIOLOGICAL OPTICS 407 

3. Obtain a luminous point as follows. In- 
sert in front of the condenser the diaphragm with 
2 mm. aperture. Place the glass slide over the 
window of the box. Pull out the draw-tube to 
make the pencil of rays convergent. Throw this 
convergent pencil into the box. Determine its 
focus by finding the place at which a clear image 
of the aperture of the diaphragm is formed upon 
a screen. This focus will serve as a luminous 
point. 

After converging to the focus, the rays will 
diverge again. Place the mirror 2.5 cm. from the 
luminous point. The luminous point will then 
lie at the principal focus of the mirror. Turn 
the mirror at a small angle with the axis of the 
pencil. 

The reflected rays will be parallel. 

Conjugate Foci. — 1. Place the mirror at a dis- 
tance from the luminous point greater than the 
radius of curvature of the mirror. 

The diverging incident rays will be reflected 
from the spherical surface to a point between the 
luminous point and the mirror. At this point a 
real image of the luminous point will be seen. 

The point from which the rays diverge, and 
the point to which they converge by reflection 
from the mirror are termed conjugate foci. 

2. Draw back the lantern and thus increase 



408 THE OUTGO OF ENERGY 

the distance between the luminous point and the 
mirror. 

As the distance between the luminous point 
and the mirror increases, the distance between 
the mirror and the image diminishes. 

Move the lantern towards the optical box, and 
thus bring the luminous point towards the mirror. 

As the distance between the mirror and one 
conjugate focus diminishes, the distance between 
the mirror and the other conjugate focus in- 
creases. As one focus approaches the mirror, the 
other recedes. 

3. Place the mirror 5 cm. from the luminous 
point. The luminous point is now at the centre 
of the sphere of which the reflecting surface is 
a segment. The incident rays are therefore all 
radial, i. e. perpendicular, to this surface. Con- 
sequently all the rays will be reflected to the 
point of origin. The incident and the reflected 
rays will coincide. The centre of the reflecting 
surface and its optical image will also coincide. 
The conjugate foci coincide. 

Virtual Image. — 1. Place the mirror at a 
distance from the luminous point less than the 
principal focal distance. 

The reflected rays will diverge. They will 
appear to proceed from a point lying behind the 
mirror. The distance between this unreal or 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 409 

virtual image and the mirror will be greater than 
the distance between the mirror and the lumi- 
nous point. As the luminous point approaches 
the mirror, its virtual image will also approach. 

2. Hold a small object nearer the mirror than 
its principal focal distance. 

Note that the image is virtual, upright, and 
larger than the object. 

Construction of Image from Concave Mirrors. — 
Determine by construction the length of the 
image of an arrow 2 cm. long, placed 10 cm. from 
the middle point of a concave mirror of 5 cm. 
radius of curvature. 

Draw a horizontal line. With any convenient 
point on this line as a centre describe an arc 
of 5 cm. radius, that shall intersect the line. 
This arc will be the section of a concave mirror. 
The horizontal line will be the principal axis, 
and the intersection of the principal axis and 
the arc, the middle point of the mirror. The 
principal focus of the mirror will lie halfway 
between the centre of curvature and the middle 
point. At right angles to the principal axis 
and 10 cm. from the middle point draw a vertical 
arrow 2 cm. long. Determine first the position 
of the image of the point of the arrow. Draw 
from the point to the mirror an incident ray 
parallel to the principal axis. This parallel ray 



410 THE OUTGO OF ENERGY 

will be reflected through the principal focus. 
Draw a second incident ray from the arrow point 
through the centre of curvature. This ray will 
be perpendicular to the spherical surface and 
will be reflected in the same line. The inter- 
section of these two reflected rays will be the 
image of the point of the arrow. 

Determine in like manner the position of the 
image of the other end of the arrow. 

Keflection from Convex Mirrors 

The laws of reflection from convex mirrors 
may be deduced from those already stated for 
concave mirrors. The image reflected from con- 
vex mirrors is virtual, upright, and smaller than 
the object. 

Determine by construction the length of the 
image of an arrow, 2 cm. long, placed 10 cm. 
from the middle point of a convex mirror of 
5 cm. radius. 

Eefraction 

1. Place the diaphragm of 2 mm. aperture in 
front of the condenser. Push in the draw-tube of 
the lantern until a beam of parallel rays enter 
the box. In the box lay the square glass bottle 
on its side upon a wooden block and at right 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 411 

angles to the pencil of light. Neglect the re- 
flected rays. 

Observe that the incident rays pass through 
the bottle and its contents, and are not bent from 
their course. Light, passing from one medium 
into another of different density, is not refracted, 
provided the course of the ray be perpendicular 
to the surface separating the media. 

2. Turn the bottle so that the incident ray 
shall enter it at an angle. 

On passing from the air into the denser 
medium of the glass and the contained liquid, 
the incident ray will be bent from its course. 
On passing from the denser medium into the air 
again, the ray will once more be bent from its 
path. Imagine a perpendicular erected at the 
points of incidence and emergence. The re- 
fracted ray will be bent toward the perpendicu- 
lar on passing into the denser medium, and away 
from the perpendicular on leaving the denser 
medium. 

Turn the bottle and thus alter the angle be- 
tween the incident ray and the perpendicular 
(angle of incidence). 

The angle between the refracted ray and the 
perpendicular (angle of refraction) increases with 
the angle of incidence. Exact measurements 
made by Snellius and Descartes, about 1621, 



412 THE OUTGO OF ENERGY 

showed that — (1) the refracted ray lies in the 
same plane with the incident ray and the per- 
pendicular, and (2) the sine of the angle of in- 
cidence stands in an unalterable relation to the 
sine of the angle of refraction. 

The sine of the angle of incidence is to the 
sine of the angle of refraction as the velocity of 
the light ray in the first medium is to its velocity 
in the second, or refracting medium. The ratio 
of the velocity of light in a vacuum to its velocity 
in any medium is termed the index of refraction, 
or refractive power of that medium. If the 
velocity of light in a vacuum be taken as 1, that 
of light in air at 0° temperature and 760 mm. 
pressure, will be 0.9997, a difference so slight 
that the velocity in air is usually taken as the 
unit. The law of refraction is commonly ex- 
pressed as follows : Let n represent the index of 
refraction, a the angle of incidence, and b the 
angle of refraction ; then 

. 7 sin a 

sm a = n sin b, or n 



sin b 



As a rule, the physically denser medium is 
also optically denser. Thus the refractive index 
for the Frauenhofer line 1 D, on passing from air 

1 White light is composed of rays of different refrangibility ; 
hence the use in such measurements of pure spectral rays. 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 413 

into crown glass, of which spectacle lenses are 
made, is 1.530; into flint glass, 1.635; into water 
at 15° C, 1.332. 

Kefraction by Prisms 

A refracting medium bounded by two plane 
surfaces not parallel is termed a prism. The 
planes are termed the refracting surfaces. The 
angle which they make with each other is termed 
the refracting angle of the prism. 

1. Place a prism in the optical box in the 
beam of parallel rays. The beam will be bent 
from its course on entering and on leaving the 
prism. The emerging pencil will be divergent, 
for the homogeneous rays, the union of which 
produces the sensation of white light, are not 
equally refracted, — the rays towards the red end 
of the spectrum are bent less strongly than those 
towards the violet end, the order being red, 
orange, yellow, green, blue, violet. 

Construction of the Path of a Ray passing through 
a Prism. — Draw a horizontal line 5 cm. in length. 
Upon this line construct the section of a prism. 1 



1 To construct the section of a prism: Let the horizon- 
tal line be the base of the prism. Place the brass leg of the 
drawing compasses at one end of the base line. Draw a circle 
of 3 cm. radius. Place the brass leg at the other end of the 
base line and draw a circle of the same radius. A line joining 
the intersections of the two circles will be perpendicular to the 



414 THE OUTGO OF ENERGY 

Draw with ink a ray incident to the refract- 
ing surface. 1 Find the sine of the angle of in- 
cidence. 2 For the Frauenhofer line D passing 
from air into crown glass the ratio of the sine 
of the angle of incidence an to the sine of the 
angle of refraction bn is 

an '. bn '.'. 1.53 I 1 

For the same light passing from crown glass 
into air the ratio of the sine of the angle of in- 
cidence to the sine of the angle of refraction is 
the reciprocal of the ratio from air to crown glass 

an I bn '.'. 1 '. 1.53 

middle of the base line. Let a point on this perpendicular 
5 cm. above the base line be the apex of the section. Join the 
apex Avith the ends of the base line. Ink the boundaiy lines of 
the cross-section thus obtained. Erase the pencil construction 
lines. 

1 For convenience let the incident ray come from the pro- 
longed base line of the prism 10 cm. from the nearest refract- 
ing surface. Let the point of incidence — the point at which 
the incident ray meets the refracting surface — be about the 
middle of the refracting surface. 

2 To find the sine : With the point of incidence as a centre 
draw a circle of convenient radius (2 cm.). Construct a radius 
of this circle perpendicular to the refracting surface at the point 
of incidence. From the intersection of the circle with the in- 
cident ray draw a line perpendicular to the radius (a line drawn 
from the point of intersection parallel to the refracting surface 
will be perpendicular to the radius). This is the sinus line of 
the angle. The ratio of this line to the radius of the circle is 
the sine of the incident angle. 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 415 

Measure the length of the sine of the angle of 
incidence in millimetres. Suppose that an in 
the present instance is 13 mm. Then with 
equation (1) 

1.53 : 1 : : 13 : x 

x — 8.5 mm., the sine of the angle of refraction. 

Find on the construction circle within the 
prism a point 8.5 mm. in a perpendicular line 
above the diameter at right angles to the refract- 
ing surface. Continue the ray through this point 
to the second refracting surface. Ink the path 
of the ray within the prism. Erase the con- 
struction lines within the prism, but leave un- 
touched those without the prism. Find the sines 
of the angles of incidence and refraction at the 
second refracting surface. Draw with ink the 
path of the emergent ray. Preserve all these 
construction lines. Write the equations in ink 
in the upper left-hand corner of the paper, and 
the four sines in the upper right-hand corner. 

The degree to which light is refracted on pass- 
ing through a prism depends on the refracting 
power of the substance of the prism, the size of 
the refracting angle, and the size of the angle of 
incidence. 



416 THE OUTGO OF ENERGY 



Effraction by Convex Lenses 

Principal Focus. — 1. Place the diaphragm of 
2 mm. aperture in the lantern. Throw a beam 
of parallel rays into the optical box. Place the 
doable convex lens in the axis of the beam about 
5 cm. from the window of the box. 

The parallel rays will be brought to their 
principal focus about 10 cm. (4 inches) from the 
lens. Note the increase in intensity as the rays 
converge. 

Place the black wooden screen at this point. 

A real image of the luminous aperture of the 
diaphragm will be perceived. 

2. Place the diaphragm of 2 mm. aperture over 
the window of the box. Direct the light of the 
lantern upon the opening in the diaphragm. 
From the illuminated opening rays will diverge 
in all directions. Place the lens 10 cm. from this 
luminous body, so that it shall lie in the princi- 
pal focus of the lens. 

The diverging rays will be rendered parallel. 
Pays diverging from the principal focus are 
rendered parallel by passing through a convex 
lens. 

A lens may be regarded as an infinite series of 
prisms. In a convex lens the refracting angle 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 417 

of each hypothetical prism is directed to the 
periphery of the lens. As the periphery is ap- 
proached the refracting angles increase, and 
hence refraction increases. The increased refrac- 
tion of the outer rays diverging from a luminous 
point compensates in part for their greater angle 
of incidence, and hence most of the rays converge 
approximately to the same focus. 

Estimation of Principal Focal Distance. — Re- 
move from the lantern the tubes holding the projec- 
tion lenses. Place in front of the condensing lens 
the diaphragm with L-shaped aperture each limb 
of which is 5 mm. long and 1 mm. broad. Place 
the convex lens in the axis of the pencil emerg- 
ing from the illuminated slit and at a distance 
from it a little greater than the principal focal dis- 
tance as determined roughly in the preceding ex- 
periment. On the other side of the lens place a 
screen at such a distance as to give a strongly 
enlarged clear picture of the L_. Measure 

I = the length of one limb of the |_, 
L = the length of its image, 
A — the distance of the screen from the lens, 
/ = the principal focal distance of the lens, 

I 



then 1 f=A 



L + l 



1 This formula is derived as follows : Let a be the distance 
27 



418 THE OUTGO OF ENERGY 

The principal focal distance of a double con- 
vex lens is approximately equal to the radius 
of curvature. 

Conjugate Foci. — Place in the lantern the dia- 
phragm of 2 mm. aperture. Be move the tubes 
holding the projecting lenses. Place the convex 
lens against the window of the optical box. 
Place the black screen twice the focal distance 
from the lens. Move back the lantern until a 
clear image of the luminous aperture appears 
on the screen. 

The point from which rays passing through 
a lens diverge, and the point to which they con- 
verge, are termed conjugate foci. Measure the 
distance of the luminous aperture from the lens. 
It will be found to be twice the focal distance. 
"When the point of divergence is separated from 
the lens by twice the focal distance, the point 
of convergence is equally distant from the other 

of the object from the principal surface of the lens (see page 46); 

then—- + -= -j-. The relation between the size of the image 
A a f 

and the size of the object is L '. I \ '. A I a ; then - = -—=, 

a A I 

and, by substitution,— = — + — -, whence / = A 



'/ A AT J L+V 

Compared with the thickness of the lens, the distance of the 
object from the lens is so great that it may be used in place of 
the unknown distance from the principal surface (Kohlrausch: 
Leitfaden der praktischen Physik, 1887, p. 142). 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 419 

side of the lens, — the conjugate focal distances 
are equal. 

Move the lantern farther from the lens. 

The conjugate focus will approach the lens. 
As one conjugate focus recedes the other ap- 
proaches the lens. 

Virtual Image. — 1. Place the 2 mm. diaphragm 
over the window of the optical box. Let the di- 
verging rays pass through the convex lens placed 
at a distance from the luminous point less than 
the principal focal distance. 

After passing through the lens, the diverging 
rays will continue to diverge though the degree 
of divergence will be less. Prolonged backwards, 
they would unite in a virtual image on the same 
side of the lens as the luminous object. The 
virtual image is farther from the lens than the 
object, is never inverted, and is always enlarged. 
(Compare the construction, directions for which 
will be given on page 421.) 

2. Look through the convex lens at printed 
words placed between the lens and its principal 
focus. 

The image is virtual and enlarged. 

Construction of Image obtained with Convex 
Lens. — The line which joins the centres of curva- 
ture of a double convex lens is termed the prin- 
cipal axis or optical axis. In every lens there 



420 THE OUTGO OF ENERGY 

are in the principal axis two points so placed 
that when the entering ray is directed toward 
the first, the emergent ray will appear to come 
from the second in a direction parallel to the 
entering ray. These are termed nodal points. 
In ordinary glass lenses the distance between the 
two nodal points is about one third the thickness 
of the lens. When this distance is so small that 
it may be disregarded, the two nodal points may 
be assumed to meet in an intermediate point 
termed the optical centre (compare page 444) of the 
lens. A ray directed to the optical centre is not 
refracted but passes through the lens in a straight 
line. The position and size of an image formed 
by a lens can be found by drawing one line from 
each extremity of the object through the optical 
centre, and another from each extremity parallel 
with the principal axis to the lens and thence 
through the principal focus. The intersections 
of these lines mark the position of the image and 
its upper and lower limit. It is necessary to 
remember that parallel rays are refracted through 
the principal focus only when the aperture of the 
lens does not exceed approximately ten degrees. 

Draw a horizontal line to serve as the principal 
axis. Let a point near the middle of the line be 
the optical centre of a double convex lens of 10° 
aperture and 5 cm. radius. The radius of curva- 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 421 

ture being 5 cm., the principal focus will lie 
approximately 5 cm. from the optical centre. 
Draw through the optical centre a line 10 mm. 
long at right angles to and bisected by the prin- 
cipal axis. Connect the ends of this line with 
the principal focus. The angle included will 
be approximately 10°. The vertical line will 
then represent a double convex lens of 10° aper- 
ture, assumed to be without thickness in order 
that the nodal points may coincide with the opti- 
cal centre. At auy distance greater than 5 cm., 
draw an arrow at right angles to and bisected 
by the principal axis. The height of the arrow 
must not exceed the diameter of the lens, so 
that rays emitted from the ends of the arrow 
parallel to the principal axis of the lens shall 
pass through the lens. From the ends of the 
arrow draw to the lens and thence through 
the principal focus incident rays parallel to the 
principal axis. From each end of the arrow 
draw a line through the optical centre of the 
lens. 

The intersections of these lines mark the upper 
and lower limits of the image. Note that the 
image is real and inverted. If the object be situ- 
ated at twice the focal distance from the lens, 
the image will be the size of the object ; if at less 
than twice the focal distance, the image will be 



422 THE OUTGO OF ENERGY 

larger than the object ; if at more than twice the 
focal distance, the image will be smaller than the 
object ; finally, if the object be situated between 
the principal focus and the lens, the image will 
no longer be real, but virtual and larger than the 
object, as mentioned on page 419. 

Befraction by Coxcaye Lenses 

Place the diaphragm with 2 mm. aperture in 
front of the condenser. Throw a pencil of paral- 
lel rays into the box. Let the rays fall upon a 
concave lens. 

The parallel rays will be rendered divergent. 

Look through the concave lens at printed 
words. The image is virtual, upright, and 
smaller than the object. It is nearer the lens 
than the object, and is always within the prin- 
cipal focal distance. 

Befraction by Segments of Cylinders 

1. Place the diaphragm with 2 mm. aperture 
in front of the condenser. Throw a pencil of 
parallel rays into the box. Place the cylindrical 
lens in the axis of the pencil in such a position 
that the curvature shall be from side to side, i. e. 
in the horizontal meridian. 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 423 

The image of the circular aperture in the dia- 
phragm will be a vertical line with blurred con- 
vex ends. 

Turn the cylinder so that the curvature shall 
be in the vertical meridian. 

The image will be a horizontal line with 
blurred convex ends. 

2. Place the diaphragm with horizontal slit in 
the lantern. Throw parallel rays into the box. 
Place the cylinder in the axis of the pencil with 
its curvature vertical. 

The horizontal line is a fusion of illuminated 
points. From each point rays diverge in all 
directions. Those passing from any point in 
vertical planes through the cylinder convex in 
its vertical meridians will be focussed by the 
convex surface in a corresponding point in the 
image. The overlapping of such points will form 
a horizontal line with clear upper and lower 
edge. The rays passing from any point in the 
illuminated line in horizontal planes through 
the cylinder with vertical curvature will be 
refracted by plane glass surfaces and will not 
come to a point but will form a faint horizontal 
line. The overlapping in the image of the 
bright points in which unite the rays passing 
in vertical planes and the faint horizontal lines 
formed by rays passing in horizontal planes will 



424 THE OUTGO OF ENERGY 

form upon the screen a horizontal line with 
blurred ends. 

Place the vertical slit in front of the con- 
denser. 

A broad, faint, horizontal line with blurred 
ends will be observed. Draw a diagram illus- 
trating the formation of this image. 

Turn the cylinder, so that the curvature shall 
lie in the horizontal meridian. 

The horizontal rays are at once united in a 
narrow sharply defined vertical line with blurred 
ends. 

Kefraction through Combined Convex and 
Cylindrical Lenses 

Thus far segments of perfect spheres or cylin- 
ders have been considered separately. In the 
eye both the cornea and the lens are frequently 
more convex in one meridian than in another. 
Such surfaces can be obtained by combining a 
convex with a cylindrical lens. 

1. Place the diaphragm of 2 mm. aperture in 
front of the condenser. Throw parallel rays 
into the box. Place the convex lens in the axis 
of the pencil next the window. Keceive the 
image of the illuminated aperture upon a screen 
placed at the principal focus. The image will be 
a well-defined circle. Place the cylindrical lens 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 425 

as close as possible to the convex lens. Let the 
curvature of the cylinder be in the vertical 
meridian. 

The circle will give place to a vertical line. 

Move the screen about 4 cm. nearer the lenses. 

The image of the circle will now be a horizon- 
tal line. 

Place the screen half way between the nearer 
and the farther focal lines. 

The image will be circular. At other points 
in the focal interval or space separating the two 
focal lines the image will be an ellipse. 

2. Hang the block containing the cylindrical 
lens on the end of the draw-tube of the lantern. 
Leave the convex lens in its former position. 
Fill the box with smoke. Let the curvature of 
the cylindrical lens be in the vertical meridian. 
Observe the pencil of rays. 

The pencil will be drawn out to a vertical line 
at the farther focus. Seen from above the cross- 
section of this line will be a bright spot. At the 
nearer focus the pencil will be flattened to a 
horizontal line. 

Eotate the cylinder through 90°. The curva- 
ture will now be in the horizontal meridian. 
Watch the pencil as the lens turns. 

As the cylinder revolves the contour of the 
pencil will change. When the curvature is 



426 THE OUTGO OF ENERGY 

finally horizontal the nearer focal line will be 
vertical, the farther focal line will be horizontal. 

Eotate the cylinder through 45°. 

By looking at the pencil first from one side of 
the box and then from the other, the focal lines 
may readily be seen in profile, as well as in 
cross-section. 

Aberration 

Spherical Aberration by Reflection. — In Fig. 
64 a concave mirror, AB, has the centre of curva- 
ture, C, and the principal focus, F. BE is one 
of several incident parallel rays. CE is perpen- 
dicular to the point of incidence. EF is the ray 
reflected from E to the principal focus, G the 



point at which the reflected ray cuts the axial 
line OK. BEWCG, therefore ZGCE=CED 



INTRODUCTION" TO PHYSIOLOGICAL OPTICS 427 

= C E G, and C G E is an isosceles triangle. Then 
if r be the radius and x the angle formed by the 
perpendicular CE with the axial ray C G, CG 

T 

— . So lon^ as angle x is small, cosine x 

2 cos x 

will be nearly 1. C G will then be nearly one 
half the radius C K. Hence incident rays near 
the axial ray C K will be reflected approximately 
to the principal focus E, which lies half w T ay 
between the centre of curvature and the mirror. 
As the aperture 1 of the mirror increases, angle x 
also increases. The larger x, the smaller will be 
the denominator of the expression for G G, and the 
greater the distance of G from C. Eays reflected 
from the outer portion of a mirror of larger aper- 
ture meet the principal axis nearer the mirror 
than those reflected from the central portion. 
The intersection of the reflected rays produces a 
curved line — the caustic curve or focal line. By 
revolving Fig. 2 about the axis C K, a caustic or 
focal surface will be obtained. 2 

Spherical Aberration by Refraction. — 1. The 
observations just made concerning concave mir- 
rors are applicable also to lenses. Eays entering 

1 The aperture is the angle included between lines drawn 
from the principal focus to the margins of the mirror or lens. 

2 Jochmann and Hermes. Grundriss der Experimental- 
physik, 1S90, p. 153. 



428 THE OUTGO OF ENERGY 

a lens with aperture greater than 10° are not 
refracted to the principal focus but cross the 
principal axis between the principal focus and 
the lens. The caustic surface formed by the 
intersection of these peripheral rays may readily 
be shown with any lens or cylinder of small 
radius of curvature. 

2. Place the diaphragm with 2 mm. aperture 
in front of the condenser. Throw parallel rays 
into the optical box. Set in the box near the 
window the cylindrical bottle of clear glass filled 
with water. The bottle will serve as a powerful 
refracting cylinder. 

The circular pencil of parallel rays will be 
brought to a focus in a vertical line (compare 
page 422). The outer rays of the pencil pass 
through the outer portion of the cylinder, and 
are therefore more strongly refracted than those 
near the optical axis, Each refracted ray inter- 
sects the refracted rays nearer than itself to the 
principal axis. These intersections form two 
curved surfaces extending from the principal 
focus — in this case a vertical line — towards 
the cylinder. On regarding these surfaces from 
above, their curvature will be apparent. 

3. Eemove the projecting lenses; place the 
ground glass plate and the diaphragm with 2 mm. 
aperture in front of the condenser. Let the rays 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 429 

diverging from the illuminated aperture pass 
through the refracting cylinder. 

The curvature of the caustic surfaces will be 
more noticeable than in Experiment 2. 

Dispersion Circles. — 1. Let the parallel rays 
pass through the double convex lens. Place a 
screen at the principal focus. A clear image of 
the circular aperture in the diaphragm will be 
seen. Move the screen away from and then 
towards the lens. 

When the screen is either nearer or farther 
from the lens than the principal focus, the image 
will be larger and less distinct. The screen will 
cut the pencil in the one case before it has con- 
verged to the focus, and in the other case after 
it has passed the focal point and is diverging. 
Under such circumstances the image of a point 
becomes a circle, termed a dispersion circle or 
circle of confusion. 

2. Substitute the diaphragm with L-shaped 
aperture for that with circular aperture. Place 
the screen a little nearer or farther than the 
focal point. 

The image will be a broad blurred line with 
convex ends. The pencils proceeding from each 
luminous point in the line will fall upon the 
screen in dispersion circles. The broad line is 
caused by the overlapping of the dispersion cir- 



430 THE OUTGO OF ENERGY 

cles. Similar blurring by dispersion circles is 
caused by the rays which pass through the outer 
parts of a lens coming to a focus sooner than 
the axial rays. 

Myopia. — In the normal eye at rest parallel 
rays are brought to a focus upon the retina. In 
the myopic eye parallel rays, and even rays to a 
certain degree divergent, are brought to a focus 
in the vitreous, whence they fall in dispersion 
circles on the retina. The most common cause 
of myopia is the abnormal length of the antero- 
posterior diameter of the eye. The defect can be 
remedied by placing a concave lens before the 
eye. The entering rays are thereby rendered 
divergent, or their divergence is increased, so that 
their focus is displaced backwards towards the 
retina. The degree of the myopia is measured 
by the strength of the concave lens which, placed 
before the eye, will bring the principal focus 
exactly to the retina. 

Let parallel rays pass through the convex lens 
of 10 cm. (4 inch) focal distance placed against 
the window of the optical box. Find the prin- 
cipal focus and then move the screen 2.5 cm. 
farther from the lens. 

The image will be blurred. The screen will 
intersect the rays diverging from the focal point. 

Hold the weak concave lens, marked — 2, in 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 431 

front of the window. This lens has a focal dis- 
tance of two dioptres or one-half metre (see 
page 435). 

The image will be clear again. The myopia 
in this case is therefore —2D. 

Hypermetropia. — In the hypermetropic eye at 
rest parallel rays and even those to a certain 
degree convergent meet the retina before they 
have come to a focus. The most frequent cause 
of hypermetropia is the abnormal shortness of the 
antero-posterior diameter of the eye. The defect 
can be remedied by placing a convex lens before 
the eye. The entering rays are thereby rendered 
convergent, or their convergence is increased. 
The degree of the hypermetropia is measured 
by the strength of the convex lens which, placed 
before the eye, will so increase its convergent 
power that parallel rays will come to a focus on 
the retina. 

Place the screen 2.5 cm. nearer the lens than 
the principal focus. 

The image will be blurred. The screen will 
intersect the rays before they have converged 
to the focal point. 

Hold the weak convex lens, marked + 2, in 
front of the window. 

The image will be clear. The hypermetropia 
in this case is therefore + 2 D. 



4 



432 THE OUTGO OF ENERGY 

Myopia and hypermetropia will be further 
considered under refraction in the eye. 

Chromatic Aberration. — The velocity of the 
homogeneous spectral rays composing white light 
is believed to be the same in a vacuum and in 
gases, but differs in transparent liquids and solids. 
The front of the light wave strikes the refracting 
surface obliquely. As the wave front enters the 
medium, its speed lessens. Thus the part of the 
front which enters first travels in the refracting 
medium at a speed less than the remainder which 
has not yet entered. The wave front is therefore 
bent towards the retarded portion. The shorter 
the wave length, i. e. the greater the wave num- 
ber, the slower will the wave advance in the 
refracting medium. Hence the wave front of the 
violet ray moves more slowly in the medium 
than the front of the red ray, and is therefore 
bent more from its course. The reverse of this 
process takes place when the wave emerges from 
the refracting medium. The violet rays are there- 
fore more refrangible than the red, and on enter- 
ing a refracting medium pursue a different path. 
Thus each spectral ray passing through a lens 
has its own principal focus. In other words, the 
images for the several spectral colors do not coin- 
cide precisely. The order in which the refracted 
spectral rays cross the principal axis is that of 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 433 

their refrangibility ; violet crosses nearest the 
lens, then blue, green, yellow, orange, and red in 
the order named. The principal focus will thus 
be a line of colors lying in the principal axis, the 
end nearest the lens being violet. The peripheral 
portions of a lens refract rays parallel to the prin- 
cipal axis more strongly than the axial portion. 
Hence the chromatic aberration will increase 
with the aperture of the lens. 

Put the ground glass plate and the diaphragm 
with 2 mm. aperture in front of the condenser. 
Let the rays from the illuminated spot of ground 
glass pass through the 10 D lens placed about 
15 cm. in front of the ground glass, i. e. a dis- 
tance somewhat greater than the focal distance 
of the lens (10 cm.). Place a white screen about 
15 cm. in front of the lens. 

The image of the white spot upon the ground 
glass will be a disk with violet centre and red 
margin. 

Eemove the white screen farther from the lens. 

At a distance of about 30 cm. the centre of the 
image will be red and the border violet. 

The image in this experiment is blurred be- 
cause the rays which pass through the peripheral 
portion of the lens cross the principal axis sooner 
than the rays which pass through the axial por- 
tion. If the screen be placed at the focus of the 

28 



434 THE OUTGO OF ENERGY 

more axial rays, this focal point in the image will 
be surrounded by dispersion circles made by the 
rays which have been refracted from the periph- 
ery through foci nearer the lens and which are 
now diverging from these foci. If the screen be 
placed at the principal focus for the peripheral 
rays, this focal point will be surrounded by dis- 
persion circles made by the rays that have not 
yet converged to the principal axis. (Compare 
spherical aberration, page 428.) 

Aberration avoided by a Diaphragm. — Place 
before the condenser the paper diaphragm with 
1 cm. aperture. 

The image at once becomes distinct, and the 
colors practically disappear. The outer rays, 
which when refracted would cross the principal 
axis far enough from the principal focus to cause 
dispersion circles, have been cut off. When the 
aperture of a lens or mirror is reduced by a 
diaphragm to 10°, the greater part of the spheri- 
cal aberration is prevented. 

Spherical aberration is still further reduced by 
combining several lenses in an objective (apla- 
natic system). 

With an achromatic lens, consisting of a col- 
lecting lens of crown glass united with a dispers- 
ing lens of flint glass, all the spectral rays may 
be brought to the same focus, and chromatic 
aberration altogether avoided. 



INTRODUCTION TO PHYSIOLOGICAL OPTICS 435 



Numbering of Prisms and Lenses 

Numbering of Prisms. — Prisms may be num- 
bered according to refracting angles or according 
to the extent to which they turn the light ray 
from its course (angular deviation). Angular 
deviation is expressed by the methods of Dennett 
and of Prentice. 

Dennett's method. — The length of an arc of 
57.295° equals its radius of curvature. A prism 
which will bend the ray one hundredth part of 
this arc is called one centrad. The angular 
deviation produced by the prisms are by this 
method expressed in hundredths of the radius 
measured on the arc. 

Prentice's method. — The unit of comparison is 
a prism-dioptre, i. e. a prism that deflects a ray 
of light one centimetre at a plane one metre dis- 
tant, or, in other words, the hundredth part of 
the radius measured on the tangent. 

Numbering of Lenses. — Lenses are numbered 
according to their refractive power. The unit is 
a lens with a focal distance of one metre. This 
unit is termed a dioptre, P. A lens of two 
metres focus is one half the refractive power, or 
\ D, The lenses ordinarily employed in ophthal- 
mic practice extend from 0.12 D to 22 D. The 



436 THE OUTGO OF ENERGY 

principal focal distance of any lens in the dioptric 
system may be found by dividing one metre, or 
100 cm., by the number of dioptres ; thus the 
focal distance of a lens of 4 D = l£& = 25 cm. 

Convex lenses are marked -f, concave lenses -. 

If two or more lenses are placed together, the 
dioptric power of the system thus formed equals 
the algebraical sum of the dioptric powers of 
the lenses in the system. 



REFRACTION IN THE EYE 437 



IX 

REFRACTION IN THE EYE 

The Eye as a Camera Obscura. — 1. From the 
eye of an ox remove the posterior part of the 
sclerotic and choroid coats over an area about 
1 cm. in diameter near the outer (temporal) side 
of the optic nerve. Cover the retina with a watch 
glass. Turn the cornea towards an incandescent 
lamp. 

A small, real, inverted image of the lamp 
will be seen upon the transparent retina. In the 
white rabbit the choroid has so little pigment that 
the retinal image may be seen without removing 
the outer coats of the eye. 

2. In a darkened room, direct a blond, blue- 
eyed individual to turn the eyes so that one 
cornea shall lie in the outer angle of the eye. 
Hold a candle near the temporal side of that 
eye. 

The small, inverted retinal image of the 
candle can often be seen shining through the 
sclerotic coat at the nasal side of the eye. 



438 THE OUTGO OF ENERGY 



The Schematic Eye 



In passing from the external air to the retina, 
the rays of light undergo refraction at the layer 
of tears on the anterior surface of the cornea, the 
surfaces bounding layers of unequal refractive 
power in the substance of the cornea, the ante- 
rior surface of the aqueous humor, the anterior 
surface of the lens, the surfaces bounding layers 
of unequal refractive power in the substance of 
the lens, and the anterior surface of the vitreous 
humor. To determine the size and position of 
visual images, it is fortunately not necessary to 
calculate refraction at each of these many sur- 
faces. The problem is much simplified by the 
following considerations. 

The irregularities in the refractive power of 
the different parts of the cornea are small ; and 
the refractive index of the layer of tears which 
covers the anterior surface is almost identical 
with the index of the substance of the cornea 
and that of the aqueous humor. Practically 
therefore the layer of tears, the cornea, and the 
aqueous humor may be regarded as a single re- 
fracting medium. Further, although the layers 
of which the lens is composed increase in refract- 
ing power towards the centre of the lens, it is 



REFRACTION IN THE EYE 439 

known that the error introduced by assuming 
the lens to be homogeneous is unimportant. 
Thus the simplified dioptric system of the eye 
consists of three refracting surfaces : the anterior 
surface of the cornea, 1 the anterior surface of the 
lens, and the anterior surface of the vitreous 
humor. The index of refraction of the aqueous 
and vitreous humors is practically the same. 

The several refracting surfaces of this optical 
system are approximately " centred," i. e. placed 
with their centres of curvature upon a right line, 
the optical axis. The diaphragm (iris) is of such 
a size and position that the rays entering the eye 
intersect the axis at small angles ; the aperture 
of the system is therefore small. Under such 
conditions it is possible to find upon the princi- 
pal axis of the system certain cardinal points, 
discovered by Gauss, by the aid of which the 
situation and size of the visual images may be 
determined. The cardinal points are (1) the an- 
terior principal focus, (2) the anterior principal 
point, (3) the posterior principal point, (4) the 
anterior nodal point, (5) the posterior nodal point, 
(6) the posterior principal focus. These points 
are reciprocal. 

As the dioptric system of the eye consists of a 

1 For convenience, the anterior surface of the cornea will be 
held to include the layer of tears. 



440 THE OUTGO OF ENERGY 

spherical surface 1 (the cornea) and a double con- 
vex lens (the crystalline lens) it will be advis- 
able to consider first the cardinal points of the 
cornea (System A), next those of the lens (Sys- 
tem B), and finally those of the two combined 
as in the eye (System C). 

Cardinal Points of the Cornea (System A) 

Construction Drawing of System A. — Draw 
a horizontal line to serve as the optical axis. 2 
Take any point, k, in this line for a centre of 
curvature. 3 From this point describe an arc 

1 The cornea is not strictly a spherical surface, but more 
nearly that produced by the revolution of an ellipse about its 
major axis. 

2 This construction drawing should be placed near the top of 
the page, in order to permit the construction drawings for the 
lens and the compound optical system to be made beneath it. 
All these drawings will be the natural size. 

3 The following list will be found convenient : 
k, centre of curvature. 

r, radius of curvature. 
h lf intersection of the first spherical surface of any system with 

its principal axis (" first " is used in the sense of nearest 

the source of light). 
h 2 , intersection of the second spherical surface with its principal 

axis. 
%!, the first medium, that which bounds the refracting surface 

on the side from which the ray comes ; also the refractive 

index of this medium. 
n 2 , The second medium, that which bounds the refracting sur- 
face on the side from which the ray emerges ; also the 

refractive index of this medium. 



REFRACTION IN THE EYE 441 

with the radius r = 7.829 mm., the radius of 
curvature of the cornea. The intersection of 
the arc with the axis is termed the principal 
point h x of the axial ray. The spherical surface 
separates two media : n v the air, and n 2 , the 
aqueous humor. 

Principal Focal Distances. — 1. Rays passing 
from the first medium through the cornea into 
the second medium unite nearly in a point, the 
posterior principal focus, <f> 2 . The distance, h x <f> 2 , 
between this point and the principal point is the 
posterior principal focal distance, F 2 . Rays pass- 
ing from the aqueous humor through the cornea 

<f>i, anterior principal focus. 

2 > posterior principal focus. 

F lt anterior focal distance. 

F 2 , posterior focal distance. 

/ l5 anterior conjugate focal distance. 

/ 2 , posterior conjugate focal distance. 

o, optical centre. 
K x , first nodal point. 
K 2 , second nodal point. 
#!, first principal point. 
M 2 , second principal point. 
5, point between two refracting surfaces at which an object 
must be in order that the images of the object formed by 
the refracting surfaces shall be similar, i. e., images of 
one another, lying therefore in the principal surfaces. 
Where con fusion might arise in applying these terms to Sys- 
tem A, B, orC, they will be distinguished by placing with them 
the letters A, B, C, respectively. Thus the anterior focal dis- 
tance of the lens will be written F x B, wherever it might other- 
wise be confused with that of System A or C, 



442 THE OUTGO OF ENEKGY 

to the air, parallel to and near the axis, unite in 
front of the cornea nearly in a point, the anterior 
principal focus, <£i. The distance, h x <j>i, between 
this point and the principal point is the anterior 
principal focal distance, Fi. The principal focal 
distances are proportional to the coefficients of 
refraction of the first and last media. The pos- 
terior principal focal distance is calculated by 
the formula 1 

(la) JP 1 = _2LL- 

ih — n i 
In comparing refractive powers the air, n v is 
taken as the unit. Thus the formula becomes 

(lb) F M = -±Z- 

The anterior principal focal distance is calcu- 
lated by tne formula 

(2 a) F x 



% r 



n 2 — n-L 
As ni — unity, the formula becomes 

< 2b > 1-S^T 

The refractive index, n u of the air = 1 ; accord- 

1 For the derivation of the formulas in this chapter the 
reader is referred to the works of Donders (Accommodation and 
Ke fraction of the Eye) and Helmholtz (Handbuch der physio- 
logischen Optik). 



REFRACTION IN THE EYE 443 

ing to Helmholtz, 1 the refractive index, n 2i of the 
aqueous humor is 1.3365 ; the ratio is |. 

Calculate F 1 and F 2 . The result is, F x = 23.266, 
F 2 = 31.095. 

2. The principal foci may also be approximately 
found by construction. Erect at the principal 
point and the nodal point 2 perpendiculars to the 
optical axis. Set off on each perpendicular dis- 
tances from the optical axis proportional to the 
rapidity of light in the first and second medium. 
The ratio in the case of the air and the aqueous 
humor is 4 : 3. Mark therefore points 20 mm. 
and 15 mm. from the axis. Draw a line from the 
20 mm. point of the first perpendicular through 
the 15 mm. point of the second, and produce the 
line to the optical axis. Its intersection with 
the optical axis is the posterior principal focus. 
Find in a similar way the anterior principal 
focus. Indicate upon the axis the cardinal points, 
remembering that the construction drawing is to 
be the natural size. 

Construction of Image. — About 10 cm. in 
front of the cornea draw an arrow, ij, which 
shall intersect the optical axis at right angles. 

1 The figures for this and subsequent calculations under " Re- 
fraction of the Eye," are those given by Helmholtz. They arc 
collected in a convenient Table on pages -461 and 462. 

12 The centre of curvature is the nodal point of a system con- 
sisting of a single spherical surface. 



444 THE OUTGO OF ENERGY 

Draw a line from the point i of the arrow 
through k. This line, since it passes through 
the centre of curvature, will coincide with the 
perpendicular to the refracting surface, and there- 
fore will not be refracted. Draw from the point 
i to the cornea a line parallel to the axis. This 
parallel ray will be refracted through the poste- 
rior principal focus </> 2 . The two rays will unite 
at their point of intersection, i 2 , which point is 
the image of i and is its conjugate focus. The 
arrow ij was vertical to the axis. Hence its 
image will also be vertical to the axis. Draw, 
therefore, from i 2 a line vertical to the axis. 
From the end j of the arrow draw a line through 
k. The intersection of this line with the verti- 
cal line just drawn will be the image j 2 of the 
point /. 

Calculation of the Position of the Conjugate 
Foci. — The conjugate foci may be found by the 
following formulas. Let f x be the conjugate 
focal distance h x i, and f 2 be the conjugate focal 
distance h x j 2 . 

(3a) A= f^T 2 < 4a > f ^J^¥ x 

For virtual images the formulas become 
(3b) /l = .** (4b) /2 = ^4 



REFRACTION IN THE EYE 445 



Cardinal Points of the Crystalline Lens 
(System B) 

Construction Drawing of System B. — When 
the lens is accommodated for distant vision the 
radius of the anterior surface is about 10 mm., 
the radius of the posterior surface about 6 mm. ; 
the thickness at the principal axis 3.6 mm. The 
index of refraction of the lens is 1.4371. The in- 
dex of the aqueous and vitreous humors is 1.3365. 

Beneath the construction drawing of the 
cardinal points of the cornea (System A) draw 
a horizontal line parallel to the optical axis 
of the cornea. This line will serve as the 
optical axis of the lens. From the intersection 
of the cornea with its optical axis let fall a 
perpendicular to the optical axis of the lens. 

The anterior surface of the lens intersects the 
optical axis 3.6 mm. posterior to the cornea. 
The radius of the anterior surface of the lens is 
10 mm. Find therefore on the optical axis a 
point 3.6 + 10 — 13.6 mm. behind the cornea. 
From this point as a centre describe an arc with 
a radius of 10 mm. that shall intersect the optical 
axis 3.6 mm. behind the cornea. A segment of 
this arc will represent the anterior surface of 
the lens. 



446 THE OUTGO OF ENERGY 

The thickness of the lens, accommodated for 
distant objects, is 3.6 mm. Mark this point. 
Here the posterior surface of the lens intersects 
the optical axis. The radius of the posterior sur- 
face is 6 mm. Find therefore a point on the 
optical axis 6 mm. in front of the posterior sur- 
face of the lens. With this point as a centre 
describe with a radius of 6 mm. the segment of 
the arc that shall represent the posterior surface 
of the lens. Mark upon this drawing the cardi- 
nal points of the lens, as follows. 

Optical Centre. — In the cornea, a simple spher- 
ical surface, rays directed to the centre of curva- 
ture, Jc, were found to pass through the refracting 
surface unchanged in direction. In thin convex 
lenses having a long focal distance it is generally 
assumed that any ray passing through a point 
within the lens termed the optical centre, o, is not 
refracted. In thick lenses, on the contrary, every 
ray excepting that coinciding with the principal 
axis is refracted (see Nodal Points). 

The optical centre is situated in the prin- 
cipal axis within the lens. In a lens bounded on 
both sides by media of equal refracting power, 
for example, the crystalline lens bounded by the 
aqueous and vitreous humors, the optical centre 
is found by dividing the axis of the lens, i. e., 
the distance between the refracting surfaces on 



REFRACTION IN THE EYE 447 

the principal axis, into two parts proportionate 
to the radii of the refracting surfaces. 
Then 

10 + 6 : 3.6 = 6 : x 

x — 1.35 mm., the distance of o from the pos- 
terior refracting surface. 
Then 

3.6 - 1.35 = 2.25 mm, 

the distance of o from the anterior refracting 
surface. 

Nodal Points. — In thick lenses (such as the 
crystalline) with short focal distance, all the rays 
except that which coincides with the principal 
axis are refracted at one or both of the spherical 
surfaces. In order to determine the path of rays 
passing through the lens it is necessary to find 
the nodal points. These are two points so placed 
that a ray directed to the first point appears on 
leaving the lens to have come from the second 
point, in a direction parallel to the entering ray. 
All rays coming from the optical centre, o, to the 
anterior refracting surface will after refraction 
appear to have come from the first nodal point, 
JTi, situated within the lens on the principal axis, 
between o and hi. Similarly, all rays from o to 
the posterior refracting surface will appear to 
have come from the second nodal point, K 2 , situ- 



448 THE OUTGO OF ENERGY 

ated between o and h 2 . Thus o and K x are con- 
jugate foci for the surface hi, and o and K 2 are 
conjugate foci for the surface h 2 . K\ and K 2 
are virtual images of o; that is, if o were observed 
through the surface Jh the image would appear 
to be Ki, while if o were observed through h 2 
the image would appear to be K 2 . As the nodal 
points are images of the same point o, they must 
therefore be images of each other. 

The first nodal point, K lt which is the virtual 
image of the optical centre, o, formed by rays 
passing from o through the anterior refracting 
surface, li x , and which lies at the conjugate focus 
of o, is situated 2.126 mm. behind the anterior 
surface of the lens (accommodated for distant 
objects). The second nodal point, K 2 , the virtual 
image of o formed by rays passing from o through 
the posterior refracting surface, h 2 , is situated 
1.276 mm. in front of the posterior surface of the 
lens (accommodated for distant objects). The dis- 
tance between the two nodal points is 0.198 mm. 

Principal Surfaces. — Within a double convex 
lens are two parallel planes, termed the principal 
surfaces. They are perpendicular to the prin- 
cipal axis and are so placed that the emerging 
ray appears to come from a point in the second 
principal surface that exactly corresponds to the 
point in the first principal surface to which the 



REFRACTION IN THE EYE 449 

entering ray is directed. Thus the point in 
the second principal surface from which the 
emergent ray appears to come is the same dis- 
tance from the axis as the corresponding point 
in the first principal surface to which the enter- 
ing ray appears to pass. In short, each principal 
surface is the image of the other, and is of equal 
size. 

To determine the position of the principal sur- 
faces there must be found between the two 
refracting surfaces a point, s, at which an object 
will form similar images with each refracting 
surface. These images being similar are images 
of each other and of equal size. The planes in 
which they lie are the principal surfaces. 

The Point s. — The point s lies between the 
two refracting surfaces at distances proportional 
to the principal focal distance of each. It will 
be remembered that the point o was found by 
dividing the distance between the two refracting 
surfaces into two parts, proportional to the radii 
of curvature of the two surfaces. In System B 
the two refracting surfaces are the anterior and 
posterior surfaces of the crystalline lens, which 
is bounded by the aqueous and vitreous humors, 
media of equal refractive power. The focal dis- 
tances of the refracting surfaces are in this case 
proportional to the radii of curvature. Thus the 

29 



450 THE OUTGO OF ENERGY 

division of the distance between the refracting 
surfaces is the same for both s and o, and there- 
fore s and o coincide. In System C, on the con- 
trary, the first medium is the air, and the last 
the vitreous humor. The principal focal dis° 
tances are proportional to the coefficients of re- 
fraction of the first and last media ; they are 
no longer proportional to the radii of curvature ; 
therefore s and o no longer coincide, and their 
images, lying in the principal surfaces and at 
the nodal points, respectively, no longer coincide, 
but must be found separately. 

Principal Points. — At the intersection of the 
principal surfaces with the principal axis lie the 
principal points, 1 H l and H 2 . The second princi- 
pal point is the image of the first. Eays which 
in the first medium are directed to the first 
principal point are directed to the second princi- 
pal point in the last medium, i. e. } after the last 
refraction. The anterior principal focal distance 
is calculated from the first principal point, and 
the posterior principal focal distance from the 
second principal point. 

Principal Focal Distances. — The posterior focal 
distance of the lens (accommodated for distant 

1 The principal points, H x and H 2 , coincide with the nodal 
points, K x and iT 2 , when the first and last media of the optical 
system have the same refractive power. 



REFRACTION IN THE EYE 451 

objects) is 50.617 mm. The anterior focal dis- 
tance is the same, for the lens is bounded by 
media of equal density. 



Cardinal Points of the Eye (System C) 

Examine construction drawings of System A 
(the cornea) and System B (the lens). System C 
must be a combination of A and B. 

Note : 1. With System C as with System A 
the first and last media have different refractive 
powers. Therefore the principal points cannot 
coincide with the nodal points. 2. The relation 
between the nodal point h of System A and 
the nodal points iTi and K 2 of System B is such 
that the nodal points of System C will lie near 
the posterior surface of the crystalline lens. 
3. The principal point h\ of System A lies on 
the anterior surface of the cornea, and the prin- 
cipal points H\ and H 2 of System B lie in the 
lens. Hence those of System C must lie in the 
aqueous humor. 4. In System C the collecting 
power of System B is added to that of System 
A. The focal distances in System C will there- 
fore be less than those of A or B. 

Principal Surfaces. — The principal surfaces are 
found from the point 5. If a perpendicular be 
drawn at s the image of that perpendicular formed 



452 THE OUTGO OF ENERGY 

by the cornea will be of equal size with the image 
of it formed by the crystalline lens. These simi- 
lar images will lie in the principal surfaces. The 
image which the cornea forms of the point s will 
be the first principal point, Hi of System C, and 
the image which the lens forms of s will be the 
second principal point, H 2 of System C. The 
point s lies between hi of System A and H x of 
System B, at distances proportional to the pos- 
terior focal distance (F 2 = 31.095 mm.), of System 
A and the anterior focal distance (F x = 50.617 
mm.) of System B. The distance between hi, which 
lies at the anterior surface of the cornea, and 
HiB, which lies 2.126 mm. behind the anterior 
surface of the lens, is 3.6 mm. (the distance be- 
tween the cornea and the lens) plus 2.126 mm. 
= 5.726 mm. This distance is to be divided in 
the proportion 50.617 : 31.095. 

50.617 + 31.095 : 31.095 :: 5.726 : x. 

a? =2.179. Hence s lies 2.179 mm. behind the 
cornea, and 5.726 — 2.179 = 3.547 mm. in front of 
the anterior principal point of the crystalline lens. 
The first or anterior principal point of the eye, 
HiC, is the virtual image of s formed by the 
cornea; it lies at the conjugate focus of s, and 
its position is determined by the formula (3 b), 
page 444. 



REFRACTION IN THE EYE 453 

F x A = 23.266 mm. 

F 2 A = 31.095 mm. 

fzA*= 2.179 mm. 



The first principal point, H\ C, is 
23.266 x 2.179 1 _ K , , . , . ,, 

31.095 - 2.179 = L?5 mm - b6hmd h the an " 
terior surface of the cornea. 

The second or posterior principal point of the 
eye, H 2 C, is the virtual image of s formed by the 
lens. It also is found by formula (3 b). 

F X B = 50.617 mm. 

F 2 B = 50.617 mm. 

f 2 jSf = 3.547 mm. 

The second principal point, H 2 G, is 

50.617 x 3.547 QQ1 , , „ . 

— — — — — 3.814 mm. before the posterior 

OU.O-L/ o.04t/ 

principal point of the lens ; this point lies 5.924 
mm. behind the cornea ; hence H 2 C lies 5.924 
— 3.814 = 2.11 mm. behind the anterior surface 
of the cornea. The distance between the two 
principal points is 2.11 — 1.75 = 0.36 mm. 

Nodal Points. — The nodal points are virtual 
images of the point o, which divides the distance 
between the nodal points of System A and Sys- 

* The distance of the object s from the refracting surface, 
in this case, the cornea. 

t The distance of the object s from the anterior principal 
point of the crystalline lens. 



454 THE OUTGO OF ENERGY 

tern B into two parts, proportional to the anterior 
focal distance of the cornea (23.266 mm.) and the 
focal distance of the lens (50.617 mm.). As K x A 
lies 7.829 mm. and K x B 5.726 mm. behind the cor- 
nea, the distance between them is 2.103 mm. This 
is to be divided in the proportion 23.266 : 50.617. 
23.266+ 50.617: 50.617:: 2.103:^. a; = 1.4408. 
Thus o lies 1.4408 mm. behind the first principal 
point of the crystalline lens (System B) and 
consequently 

5.726 + 1.4408 = 7.167 mm. 
behind the cornea. 

By formula (3 b), Ki C, the first nodal point or 
the image of o formed by the cornea, is found to be 

23.266 x 7.167 a ^ , , . , ■ 

01 nnr w^tt^ — 6.97 mm. behind the cornea. 

«31oU9o — 7.1o7 

The second nodal point, K 2 C, or image formed 

, . 50.617 X 1.4408 

of o by the crystalline lens, is 50617 _ i 4408 

= 1.401 mm. behind the second principal point 
of the crystalline lens, and consequently 5.924 
+ 1.401 = 7.33 mm. behind the cornea. 

The distance KxK% between the first and 
second nodal points of System C -is 7.33 — 
6.97 = 0.36 mm. The distance Hi Ho = Zi K 2 . 

Principal Foci. — Bays falling on the cornea par- 
allel to the principal axis are refracted by hi A and 



REFRACTION IN THE EYE 455 

converged to the point <\> 2 A, situated 31.095 mim 
behind the cornea. On their way they are further 
refracted by System B. Hi B is 5.726 mm. behind 
the cornea. The point <£ 2 A is 31.095 — 5.726 
= 25.369 mm. behind H x . Calculated from H 2 B, 
the posterior principal focal distance F 2 of System 
B is 50.617 mm. The posterior focal distance of 
System C is calculated by the formula 
. fiF 2 . 25.369x50.617 ., QQQ 

A = f^~F. A = 2 5.369 + 50.617 = 168 " mm ' 

behind H 2 B, and hence 16.899 + 5.924 = 
22.823 mm. behind the cornea, and 22.823 - 
2.11 = 20.713 mm. behind H 2 of System C. 
The posterior principal focal distance of the eye 
is therefore 20.71 mm. 

Parallel rays falling on the posterior surface of 
the lens are refracted by the lens and converge 
at a point c^ B — 50.617 mm. in front of Hi B. 
They meet the anterior surface of the cornea 
50.617 - 5.726 = 44.891 mm. from H x B. They 
are further converged by the cornea to 

23.266x44.891 , 0fTr 
31.095 + 44.891 = lo ' 75 mm ' 

before the cornea, or 13.75 + 1.75 = 15.5 mm. 
before H x C. The anterior principal focal dis- 
tance of the eye is therefore 15.5 mm. 1 

1 In this discussion I have followed closely, in some places 



456 THE OUTGO OF ENERGY 



Calculation of the Situation and Size of 
Dioptric Images 

Draw perpendiculars through the optical axis 
of System C at the following points : the anterior 
principal focus, (/>i C, the first principal point, 
JSi C, the second principal point, H 2 C, and the 
posterior principal focus, <£ 2 C (retina). Mark on 
the optical axis the first and second nodal points, 
K x C and K 2 C. 

The following facts should be borne in mind : 

1. Every ray which in the first medium is 
directed to the first nodal point appears in the 
last medium to come from the second nodal 
point and is parallel to its original direction. 

2. The point at which the ray cuts the second 
principal surface is the same distance from the 
optical axis as the point at which the ray cuts 
the first principal surface ; between the prin- 
cipal surfaces the ray is parallel to the optical 
axis. 3. All rays parallel in the first medium 
unite in one point in the second or posterior focal 
surface (the plane passing through the posterior 
principal focus vertical to the optical axis) ; if 

almost literally, the valuable works of Donders (Accommodation 
and Refraction of the Ej T e, New Sydenham Society, London, 
1864) and Helmholtz (Handbuch der physiologischen Optik, 
2te Auflage, 1896). 



REFKACTION IN THE EYE 457 

these rays be parallel to the axis they will unite 
in the posterior principal focus. Conversely, all 
rays parallel in the second medium unite in one 
point on the first or anterior focal surface, and if 
parallel to the axis they unite at the anterior 
principal focus (Gauss). 

1. Find the course in the vitreous humor of 
any ray, a b, which enters the eye. 

Draw in the first medium a ray, a' h\ parallel 
to a b, directed to the first nodal point. In the 
second medium draw this ray, parallel to its origi- 
nal direction, from the second nodal point to the 
posterior focal surface. Then a b must also meet 
the posterior focal surface at this same place ; for 
all rays parallel in the first medium converge in 
the second medium to one point in the posterior 
focal surface. Produce ab to the first principal 
surface, thence, parallel with the optical axis, to 
the second principal surface, thence, through the 
vitreous humor, to the point already found in the 
posterior focal surface. 

2. Let i be any point in the first medium (the 
air). Find its image (for convenience i should 
be placed at least 10 cm. in front of the cornea). 

Draw from i a ray, iij\, through the first and 
second nodal points, as directed above. Draw 
from i a second ray, i 2 j2, parallel with the optical 
axis. This ray will cut the second focal surface 



458 THE OUTGO OF ENERGY 

at the principal focus. Produce i 2 j-2 until it meets 
iiji. The point of intersection will be the image 
of the point i. 

Eeduced Eye 

The distance of less than one fourth millimetre 
which separates one principal point from the 
other is so small that it may be neglected with- 
out any error of practical importance. Thus the 
two principal points may be combined in one point 
lying 2.34 mm. behind the anterior surface of the 
cornea of the normal. 1 Similarly the two nodal 
points may be combined in one point lying 
0.48 mm. in front of the posterior surface of the 
lens, or about 16 mm. in front of the retina. 
The nodal point k of the cornea (System A) is 
about 14 mm. in front of the retina. The nodal 
point of the lens and that of the cornea are com- 
bined in the reduced eye in a nodal point situated 
15 mm. from the retina. The lens may therefore 
be omitted. Indeed, the cornea is normally the 
principal refracting surface ; its focal distance is 
31.095 mm., while that of the crystalline lens is 
50.617 mm. ; if the lens were not present, parallel 
rays entering the eye would be focussed by the 

1 Listing: "Wagner's Handworterbuch der Physiologie, 1853, 
iv., p. 495. 



REFRACTION IN THE EYE 459 

cornea in a point about 10 mm. behind the retina. 
Thus the eye is reduced to a single refracting 
surface, the cornea, separating two media, the air 
and the vitreous humor. The index of refraction 
of these media is -|. The principal focal distances 
are proportional to the coefficients of refraction 
of the first and last media; F\ is 15 mm. and i\ 
20 mm., measured from the principal point. The 
visual axis (from the cornea to the retina of the 
reduced eye) is therefore 20 mm. In order to 
bring parallel rays to a focus at 20 mm., the 
index of refraction being |, the radius of curva- 
ture of the cornea of the reduced eye should be 
5 mm. 

In such a reduced eye the retinal images have 
the same position and size as in the ordinary 
eye. The reduced eye is shown in normal size 
in Fig. 65. 




Fig. G5. The reduced eye. Normal size (Donders). 

K is the optical centre or nodal point. 
h, the principal point. 

Kh = 5 mm., the radius of curvature of the 
refracting surface. 



460 THE OUTGO OF ENERGY 

</> 1? the anterior principal focus, — the focus of 
rays parallel in the vitreous. 

c£ 2 , the posterior principal focus, — the focus 
of rays parallel in the air. 

h 4>i = F x , the anterior focal distance, = 15 mm. 

h cf> 2 = F 2 , the posterior focal distance, = 20 mm. 

in _ 4 _ I\ _ 20 
n 1 ~3~ J\ ~ 15' 

With the reduced eye many calculations may 
be rapidly and easily performed. 



KEFRACTION IN THE EYE 



461 



AVERAGE MEASUREMENTS OF NORMAL 
(EMMETROPIC) EYE* 







mm. 






12 
4 


Mean diameter of pupil . . . 








1 


Thickness of lens accommodated for near 


objects 




4 


Thickness of lens accommodated for distant 








3.6 


Thickness of retina at fundus . 




0.2-0.3 


Distance between retinal vessels and rod 




and cone layer .... 




0.2-0.3 


Diameter of optic disk 


1.5 


Diameter of yellow spot . . . 




1.25 


Diameter of fovea centralis . „ 


. 


0.22 


Diameter of cone in fovea 




0.004-0.005 
0.0018 


Diameter of rod . . . . 




Accommodated for 


Distant 


Near 




objects. 


objects. 


Refractive index of aqueous 






and vitreous humors . . 


1.3365 


1.3365 


Total refractive index of crys- 






talline lens 


1.4371 


1.4371 


Radius of curvature of cornea . 


7.829 


7.829 


Radius of curvature of ante- 






rior surface of lens . . . 


10.00 


6.0 


Radius of curvature of poste- 






rior surface of lens . . 


6.0 


5.5 



1 It should be understood that the figures given in this table 
are the mean of numerous observations. The variation in 
different eyes is considerable, though in most eases not groat 
enough to be of practical importance. 



462 



THE OUTGO OF ENERGY 





Accommodated for 


Distant 


Near 




objects. 


objects. 


Distance from anterior surface 






of cornea to anterior sur- 






face of lens 


3.6 


3.2 


Distance from anterior surface 






of cornea to posterior sur- 






face of lens 


7.2 


7.2 


Calculated 






Anterior principal focal dis- 






tance of cornea . . . . 


23.266 


23.266 


Posterior principal focal dis- 






tance of cornea .... 


31.095 


31.095 


Anterior and posterior princi- 






pal focal distance of lens 


50.617 


39.073 


Distance of anterior principal 






point of lens from anterior 






surface of lens .... 


2.126 


1.989 


Distance of posterior principal 






point of lens from poste- 






rior susface of lens . . . 


-1.276 


-1.823 


Distance of the two principal 






points of lens from each 






other 


0.198 


0.188 


Posterior principal focal dis- 






tance of eye 


20.713 


18.689 


Anterior principal focal dis- 






tance of eye 


15.498 


13.990 


Distance from anterior sur- 






face of cornea to 






First principal point . . . 


1.753 


1.858 


Second principal point . . 


2.106 


2.257 


First nodal point .... 


6.968 


6.566 


Second nodal point . . . 


7.321 t 


6.965 


Anterior principal focus 


—13.745 ' 


-12.132 


Posterior principal focus 


22.819 


20.955 


Distance upon optical axis 






from anterior surface of 






cornea to retina . . . 


23.0 


23.0 



In accommodation a clear image of an object 152 mm. in 
front of the cornea, or 140 mm. in front of the anterior prin- 
cipal focus, will be formed upon the retina. 



REFRACTION IN THE EYE 463 



Eelations of the Visual Axis 

It has already been stated that the refracting 
surfaces of the eye are centred, often imperfectly, 
upon a right line, the optical axis. This line 
normally meets the retina between the yellow- 
spot and the optic papilla or exit of the optic 
nerve. To see a luminous point clearly, the 
image of the point must fall on the centre of the 
yellow spot. The line passing from the centre of 
the yellow spot through the nodal point to the 
luminous point is termed the visual axis. Unless 
the luminous point already lie in the visual axis, 
it must for distinct vision be brought there by 
the rotation of the eyeball. The object is then 
said to be "fixed" by the eye. The point about 
which the eye rotates is the centre of rotation. 
The line between the luminous point and the 
centre of rotation is the line of fixation. 

The line of fixation and the visual axis should 
nearly coincide. Generally, the visual axis 
and the optical axis do not coincide. In other 
words, the visual axis is generally a secondary 
axis, and the planes of the refracting surfaces 
are oblique to it. The optical axis passes to 
the inner side of the yellow spot. It inter- 
sects the visual axis at the nodal point. Hence 



464 THE OUTGO OF ENERGY 

the nodal point becomes the vertex of an 
angle, the angle gamma, 7, the legs of which 
are the anterior portion of the optical and visual 
axes. The angle 7 usually reaches 5°, but may 
reach 10°. 

In emmetropia and hyper metropia, the visual 
axis passes through the cornea on the inner side 
of the optical axis ; angle 7 is then positive. The 
eyeball must rotate outwards in order to fix an 
object. Thus the visual axes seem to diverge. 
Hence the angle 7 must be considered in esti- 
mating the degree of a divergent squint. 

In myopia, the visual axis may coincide with 
the optical axis or pass through the cornea on 
the outer side of the optical axis. In the latter 
case, angle 7 is negative. In this condition the 
eyeball must rotate inwards in order to fix the 
object. The deviation inwards may be confused 
with convergent squint. 

Draw a diagram showing angle 7. 

Visual Angle. — Draw an arrow in front of a 
diagram of the reduced eye. Draw lines from 
the nodal point through and beyond the two ex- 
tremities of the object. 

The angle included between the lines drawn 
from the nodal point to the extremities of the 
object is termed the visual angle. 

Apparent Size. — Within the lines marking the 



REFRACTION IN THE EYE 465 

visual angle draw a second arrow parallel to the 
first and twice its distance from the nodal point. 
Produce the visual lines from the nodal point to 
the retina. 

Observe that the retinal images of the large and 
the small arrow are of equal size. The two ob- 
jects subtend the same visual angle. Thus the 
apparent size of an object depends upon the visual 
angle. 

Size of Retinal Image. — In the emmetropic eye 
( the eye accommodated for distant vision ) the 
size of the object B is to the size of the retinal 
image h as the distance from the object to the 
nodal point of the reduced eye, g 1} is to the dis- 
tance from the nodal point to the retina, g 2 . 

(5) B : b :: g 1 : g 2 

The retinal image is smaller than the object by 
the number of times g 2 = 15 mm. is contained in 
the distance, in millimetres, of the object from the 
nodal point. 

Calculate the size of the retinal image of a 
post one metre high placed 300 metres from the 
observer's eye. 

Acuteness of Vision. — Draw upon the visual 
axis of the reduced eye a series of arrows of equal 
size, each bisected by the axis. Draw lines from 

30 



466 THE OUTGO OF ENERGY 

the extremities of these arrows to the nodal 
point. 

Observe that as the object recedes from the 
eye the visual angle and the retinal image become 
smaller. When the visual angle is less than 
one minute, the retinal image will be too small 
to be perceived ; the limit of perception will be 
reached. 

Smallest Perceptible Image. — On a black card 
gum one millimetre apart, and parallel with each 
other, two slips of white paper one millimetre 
in width. Place the card about six metres in 
front of a window or other sufficient light. Face 
the card and move backward until the millimetre 
space between the two white slips disappears be- 
cause the slips can no longer be seen separately. 
Measure the distance g-^ from the object to the 
nodal point. Calculate the size of the retinal 
image (formula 5). Compare this result with 
the diameter of the cones in the region of dis- 
tinct vision (page 461). 

Measurement of Visual Acuteness. — Taking 1' 
as the average smallest visual angle at which an 
object is perceptible, Snellen built up a set of 
test letters by combining small squares each of 
which subtends an angle of V. Thus the lines 
of which the letters are formed subtend an angle 
of 1'. The spaces between the lines also subtend 



KEFRACTION IN THE EYE 467 

this angle. Only such letters are used as can 
be drawn approximately within a square that 
shall contain twenty-five of the smaller squares, 
and shall subtend an angle of 5'. Thus the 
strokes and, so far as possible, the spaces between 
the strokes are one fifth the size of the letter. 
The size of the letter the perception of which 
constitutes normal vision at a given distance 
(that is, the letter that subtends a visual angle 
of 5' at the given distance) is obtained by multi- 
plying the distance by 0.001454 mm., which is 
the tangent * of the angle of 5'. At the distance 
of one metre the size of the standard letter is 
1000 X 0.001454 = 1.45 mm. Near each of Snel- 
len's test letters is recorded the distance viewed 
from which the letter will subtend a visual angle 
of 5' in the emmetropic eye. 

As some of the letters are not easily recognized 
by the astigmatic eye (D, for example, being some- 
times mistaken for B), the acuteness of vision 
should not be pronounced normal unless each 
letter of the entire series can be read at the dis- 



1 To obtain the tangent of an angle draw a circle with the 
vertex of the angle as the centre. The two legs of the angle 
are radii of the circle. Draw a perpendicular (tangent line) 
from the end of one radius to the prolongation of the other. 
Divide the length of the perpendicular by the length of the 
radius ; the quotient is the function called the tangent of the 
angle- 



468 THE OUTGO OF ENERGY 

tance corresponding to the number of the series. 

The acuteness of vision is expressed by — ; where 

d is the greatest distance at which the letters 
in any line are seen distinctly by the eye exam- 
ined, and D the distance at which they can be 
seen by the normally acute eye. 

Place the subject in a well-lighted room six 
metres (approximately 20 feet) in front of a 
card of Snellen's test types. Bays from an object 
six metres distant are practically parallel. At 
this distance the letters numbered VI should 

be read. If they are clearly visible, Y = - ; acute- 
ness of vision is normal. If the subject at 6 metres 
cannot see distinctly letters larger than those 

marked XVIII metres (approximately 60 feet), 
/? 

V = — ; acuteness of vision is one third the 
18 

normal. 

In some eyes vision is so acute that types 

constructed with a visual angle of 4 minutes 

(| the normal angle) can be seen clearly. 



REFRACTION IN THE EYE 469 



Accommodation 



Accommodation. — Look at any distant object. 

The object will be seen clearly. The (practi- 
cally) parallel rays proceeding from the object 
are brought to a focus on the retina. 

Look at an object ten inches from the eye. 

The rays proceeding from this object are evi- 
dently divergent, yet the object is seen clearly. 
The divergent rays have also been focussed on 
the retina. This power of voluntarily bringing 
divergent rays to a focus on the retina is termed 
accommodation. 

Schemer's Experiment. — With a fine needle 
pierce in a card two holes at a distance from each 
other a little less than the diameter of the pupil 
(average 4 mm.). Hold the card with the holes 
horizontal and near the pupil. Look through the 
holes at a pin or needle held vertical about 15 cm. 
(6 inches) in front of the eye. 

The needle will be seen clearly. 

Move the index finger over one of the holes. 

There will be no change except that the visual 
field will be darker. 

Fix a distant object, for example, a cloud. 

The needle will appear double, and each image 
will be rendered indistinct by dispersion circles, 

Move the index finger over the left-hand hole. 



470 THE OUTGO OF ENERGY 

The riglit-hand image will disappear. 

Hold the needle about 100 cm. away and fix 
some nearer object. The needle will appear 
double. Close the left-hand hole. 

The left-hand image will disappear. 

Draw a diagram to explain these observations. 
Eemember that a separate image of the needle 
will be formed by the rays passing through each 
hole in the card. 

Dispersion Circles. — Place a printed page 
about two feet in front of one eye, and shut the 
other eye. Observe the letters through a piece 
of wire gauze held six inches in front of the eye. 

Either the wire or the letters can be distinctly 
seen, but not both at once. If the letters are 
seen clearly, each wire will appear as a broad 
indistinct line made up of superposed dispersion 
circles and vice versa. 

Diameter of Circles of Dispersion. — 1 . If the 
eye be accommodated for objects at an infinite 
distance (practically twelve metres or more), the 
image of a near object will fall behind the 
retina. The image will lie in the conjugate focus 
of the object, and the position of the image can 
be calculated by the formula for conjugate foci 
(page 444). From this formula may be derived 



REFRACTION IN THE EYE 471 

y =/ 2 — F 2 , the distance from the retina to the 

image behind it. 
g, the distance from the anterior focus $1 to the 

object. 
</> x lies 20 mm. from the nodal point K. 
F 2 F v in the reduced eye, is 20 x 15 = 300 mm. 
from K. 

Find the distance behind the retina of an 
image whose object is 320 mm. from K. 

The distance is 1 mm. 

2. If y is known, the diameter of the dispersion 
circles can be calculated. In the example just 
given, the pencil of rays diverging from each 
luminous point in the object was reunited in a 
single point one millimetre behind the retina. 
At the retina, the converging cone had a certain 
section, i. e. the circle of dispersion. The base of 
the cone is evidently the pupil, which in the 
reduced eye is taken to be 19 mm. in front of the 
retina and 4 mm. in diameter. 1 

The length of y divided by the length of the 
whole cone (19 mm.), gives the proportion in 

1 The diameter of the cone is not precisely that of the pupil. 
The rays in the vitreous would appear to come from the image 
of the pupil formed by the lens. Thus the diameter changes 
from 4 to 4.23 mm. At the same time the position of the base 
is changed from 3.6 mm. (the distance of the plane of the pupil 
behind the cornea) to 3.7 behind the cornea. This brings the 
base of the cone 19 mm. in front of the retina, which is the 
position assumed for it in the reduced eye. 



472 THE OUTGO OF ENERGY 

which the diameter of the cone at its base 
(4 mm.) is reduced at the retina. In the example 
taken y = 1 mm. Then the proportion sought is 
1 : 19 + 1 = 2V Thus the diameter of the dis- 
persion circle is 2V °f 4 mm. = J mm. 

3. Calculate the size of the dispersion circle 
produced by an object twelve metres from the 
emmetropic eye. At this distance the dispersion 
circles are so small as to cause no perceptible 
lack of clearness in the image. 

Accommodation Line. — Hold a needle two 
inches from a printed page. Bring the eyes as 
near the needle as is possible without causing the 
image of the needle to blur. When the needle 
is at this " near point " of accommodation it will 
be seen clearly, but the printed words will be 
indistinct. Draw back the eyes gradually. 

Soon a point will be reached at which both 
needle and print will be seen distinctly. The 
greatest distance between two objects on the 
visual line at which the two may both be seen 
clearly while the eye is accommodated for either, 
is called the accommodation line. The length of 
the accommodation line increases as the object is 
removed from the eye. 



EEFRACTION IN THE EYE 



473 



Mechanism of Accommodation 

Narrowing of Pupil. — 1. Watch the pupil while 
the subject accommodates first for a distant and 
then for a near object. 

In accommodation for near objects the pupil 
contracts. 

2. Hold a pencil about thirty centimetres in 
front of one eye. Close the other eye. The 
pencil is seen clearly. Move the pencil towards 




Fig. 66. 



the eye until its image becomes indistinct from 
dispersion circles. Now observe the pencil 
through a pin-hole in a card placed in front 
of the pupil. 

The image is sharper. The size of the dis- 
persion circles is diminished by making the 
aperture smaller and thus cutting off the rays 



474 THE OUTGO OF ENERGY 

that meet the refracting surfaces at a distance 
from the optical axis (compare page 434). 

Relation of Iris to Lens. — 1. Stand the convex 
mirror upright on a level with the eye of the 
observer. Over the mirror (Fig. 66, C M) place 
a diaphragm of black paper, I V, with an aperture, 
PP', four millimetres in diameter. Let this aper- 
ture be the pupil and the convex mirror be the 
crystalline lens. The wooden block in which the 
mirror is held will support the diaphragm so that 
there will be a space between the border of the 
pupil and the surface of the mirror. Let the 
lamp, L, be on one side of the aperture and 
the observer's eye, E, on the other. By means 
of the convex lens of 6.5 cm. focal distance fur- 
nished with the ophthalmoscope concentrate the 
light upon the margin of the pupil in the direc- 
tion LH. It will pass the margin P and be 
reflected from the mirror to the eye in the direc- 
tion H E. No rays from L can reach the mirror 
between H and C. This portion of the mirror 
will reflect the posterior side of the diaphragm. 
Thus the light from S falling on the mirror at J 
will be reflected in the direction JE to the ob- 
server's eye, and a dark band, the image of the 
back of the diaphragm, will appear in the mirror 
between the image of L at H and the margin of 
the pupil. 



REFRACTION IN THE EYE 475 

Depress the paper diaphragm until the margin 
of the pupil lies against the mirror. The black 
line will disappear, because the ray J E, reflected 
from the back of the diaphragm, is intercepted. 
The space PH is closed (Helmholtz). 

2. In a dark room repeat Experiment 1 upon 
the eye. The iris will be the diaphragm, I V, and 
the anterior surface of the crystalline lens will 
be the convex mirror. The light and the ob- 
server's eye should be placed as in Fig. 66. 

The bright image of the light formed by the 
cornea, should be neglected. Near this image 
are two others, very much fainter. The larger 
of the two is indistinct and upright ; it is re- 
flected from the anterior surface of the crystal- 
line lens. The smaller is a sharp, inverted image 
from the posterior surface of the lens. By mov- 
ing the glass lens the light may be thrown at 
will on all parts of the border of the pupil. 

No dark line or image of the posterior surface 
of the iris will be seen. The margin of the iris 
lies upon the lens. 

Changes in the Lens. — 1. Direct the subject to 
cover one eye. Place a needle at the near point 
of the other eye in line with some distant object 
that can be clearly seen. The two objects must 
be kept accurately in line throughout the experi- 
ment. Let the observer stand at one side of and 



476 THE OUTGO OF ENERGY 

a little behind the subject, so that he shall see 
about half of the corneal image of the black 
pupil of the subject's eye projecting beyond the 
corneal border of the sclera. Note, from within 
outwards, the optical section or profile of the 
margin of the sclera, the anterior half of the 
pupil, a clear portion of the cornea, and finally 
a dark stripe which is the most anterior portion 
of the cornea. 1 

Watch carefully the clear interval between this 
dark stripe and the profile of the pupil while the 
subject, keeping the eye steadily in one position, 
accommodates first for the distant and then for 
the near object. 

The interval between the corneal stripe and 
the border of the pupil diminishes on accommo- 
dation for near objects. Hence the border of the 
pupil moves forward. If this were not the case, 
the interval would become larger, for the pupil 
narrows in accommodation. Accidental turning 
of the subject's eye towards the observer would 
also cause the interval to appear larger. As the 
margin of the iris lies upon the lens, this obser- 
vation is evidence that the anterior surface of the 

1 The sclera projects over the iris. The inner surface of the 
projecting portion is in shadow. The profile view of the image 
formed of this projecting portion by the refraction of the cornea 
is the dark line observed in the above experiment. It is dark 
by contrast with the image of the well-lighted iris. 



REFRACTION IN THE EYE 477 

lens moves forward in accommodation (Helm- 
holtz). 

2. Place the diaphragm with L-shaped aper- 
ture in the lantern. In a dark room place the 
lantern in front and to the inner side of the 
subject's eye, so that the rays shall make an angle 
of about 40° with the visual axis of the eye 
directed forwards. Let the observer's eye be in 
a corresponding position to the outer side of the 
subject's eye. In the visual axis of the subject's 
eye place an object at the near point and one at 
the far point (six metres). Let the subject 
accommodate for the far point. 

Note the sharp, very bright, upright image 
reflected from the cornea, the indistinct, faint, 
upright, slightly larger image from the convex 
anterior surface of the crystalline lens, and lastly, 
the sharper, faint, inverted, small image reflected 
from the concave posterior surface of the lens. 1 
The image from the anterior surface of the lens 
lies apparently 8-12 mm. behind the pupil, and 
therefore disappears behind the border of the 
iris upon slight changes in the position of the 
light or the observer's eye. The image from 
the posterior surface lies apparently about 1 mm. 

1 These images may be magnified with advantage by looking 
at them through the lens of 7.5 cm. focal distance furnished 
with the ophthalmoscope. 



478 THE OUTGO OF ENEKGY 

behind the pupil, and therefore is not much dis- 
placed towards the pupil and the corneal image 
upon slight movements of the light or the ob- 
server's eye. 

Let the subject accommodate for the near point. 

The image from the anterior surface of the 
lens will become considerably smaller, and usually 
it will approach the middle of the pupil. The 
image formed by a convex mirror becomes smaller 
the smaller the radius. Hence in accommoda- 
tion the anterior surface of the lens becomes 
more convex. 1 

The image from the posterior surface also 
becomes smaller, but the change is too slight 
to be observed by the method employed in this 
experiment. Some diminution in size would be 
expected from the shifting of the cardinal points 
in accommodation. Exact measurements with 
the ophthalmometer show that the change is too 
great to be explained in this way. 

Thus in accommodation the focal distance of 
the lens is shortened and its principal points 
move forwards. 

1 If in accommodation the anterior surface approached the 
cornea, the image would become smaller through refraction in 
the cornea, even though the anterior surface did not become more 
convex. Calculation shows that the change thus produced is 
very small relative to that actually observed in the above 
experiment. 



REFRACTION IN THE EYE 479 



Measurement of Accommodation 

Far Point. — The most distant point of which 
the eye at rest, i. e. the ciliary muscle entirely 
relaxed, can form a clear image on the retina was 
termed by Bonders the far point (punctum re- 
motum = r). The distance of r from the eye 
= B. In the emmetropic eye parallel rays are 
brought to a focus on the retina ; r is theoret- 
ically at an infinite distance. Practically, if the 
accommodation be kept at rest by voluntarily re- 
laxing the ciliary muscle or by paralyzing the in- 
nervation of the muscle with atropine, the far 
point will be found at twelve metres, at which 
distance objects produce dispersion circles so 
small as to cause no perceptible lack of clearness 
in the image. 

In the myopic eye, r is a short distance in front 
of the eye. 

In hypermetropia, only convergent rays can be 
focussed on the retina of the eye at rest. Parallel 
and divergent rays can be focussed only by use 
of the accommodation mechanism ; r is therefore 
negative. 

Determination of Far Point. — Place the subject 
in a well-lighted room six metres in front of a 
card of Snellen's test-types. At this distance the 



480 THE OUTGO OF ENERGY 

normal eye can read the letters numbered VI 
If the subject sees these letters clearly the acute- 
ness of vision is normal, and R is infinite. If the 
subject reads I at one metre, II at two metres, 
but cannot read VI at six metres, bring the test 
card towards the eye until a point is reached at 
which the letters numbered VI are seen clearly. 
This is the far point. 

Near Point. — 1. look through the holes in 
the card used for Scheiner's experiment at a 
needle placed vertically about 30 cm. (twelve 
inches) in front of one eye. Obtain a single 
clear image of the needle. Bring the needle 
nearer the eye. As the distance between the 
needle and the eye becomes shorter, the rays pro- 
ceeding from the needle become more divergent 
and require a greater convexity of the lens to 
bring them to a focus on the retina. A point 
will be reached at which the divergence exceeds 
the utmost converging power of the dioptric ap- 
paratus and the images received through the two 
holes in the card can no longer be made to co- 
incide on the retina ; the needle will then appear 
double. This is the near point of accommodation 
(punctum proximum — p). The distance from p 
to the eye = P. 

Determination of Near Point. — Hold in front of 
the eye a test card containing print so small that 



REFRACTION IN THE EYE 481 

it shall subtend the standard angle of 5' when 
placed 25 cm. from the cornea. The distance from 
the eye at which this type can be read clearly 
= P. 

Range of Accommodation. — The range of accom- 
modation is the expression of the total accommoda- 
tive power of the eye. With the eye at rest rays 
diverging from the far point r are brought to a 
focus on the retina. With the ciliary muscle 
fully contracted, rays diverging from the near 
point p are focussed on the retina. To bring the 
more divergent rays from p to the same focal 
plane as the less divergent rays from r, an auxiliary 
lens must be employed, as in the following ex- 
periment. 

Place the diaphragm with L-shaped aperture 
in front of the condenser. Remove the tubes 
holding the projecting lenses. Rays will now 
diverge from the illuminated I Place this illu- 
minated object at a convenient far point, for ex- 
ample, 26 cm. in front of the convex lens of 10 cm. 
focal length. Place a screen at the conjugate 
focus. Note the clear image. Move the object 8 cm. 
nearer the lens. Let this be the near point. The 
conjugate focus now falls behind the screen and 
the image is blurred by dispersion circles. Place 
in front of the 10 D lens an auxiliary lens of + 2 
D. The image will be clear. The rays diverg- 

31 



482 THE OUTGO OF ENERGY 

ing from the near point will be united by the two 
lenses in the same focal plane in which the rays 
diverging from the far point were united by the 
first lens. The second lens has " accommodated " 
the optical system to the distance R — P. 

In this experiment the power of the +2D lens 
represents the distance R — P, or range of accom- 
modation. The power of a lens is inversely pro- 
portional to its focal distance A. Consequently, 

the range of accommodation 2 = 1 : A or -7. Then 
& A 

A~ R~R 

In the eye the auxiliary lens necessary for 
focussing the rays diverging from the near point 
is provided by an increase in the convexity of the 
crystalline lens. The difference in refractive 
power of the two lenses (the crystalline in its 
least convex form and the crystalline in its most 
convex form) is the measure of the range of 
accommodation of the eye. If the lens remain in 
its least convex form, an auxiliary lens must be 
placed before the cornea in order to bring rays 
diverging from an object at the near point to a 
focus on the retina. The strength of this auxil- 
iary lens becomes then the practical measure of 

1 When 1 = 1 metre 



REFRACTION IN THE EYE 483 

the range of accommodation, and— - = — — — 

A Jr K 

becomes its numerical expression. 1 

In myopia P may be 10 cm. and R 25 cm. 

myopia is of 4 dioptres, -r =10 D-4D = 6D. 

In this case Pis greater than A. 

In hypermetropia P may be 50 cm. and B neg- 

ok ™ 1 10 ° o-n a 1 10 ° 

ative, — 25 cm. Then — = — - = 2 D, and — = - 7 r- 

P 50 P —25 

= — 4 D. The hypermetropia is of 4 D. — = 

2 - (-4 ) = 2 + 4 = 6 D, which is the sum of 
P and P. 

In emmetropia P may be 20 cm. and R in- 
finite. Then ^ = -. — = -^~ = 5 D. In 

1 Theoretically the auxiliary lens should be placed in the 
eye and not in front of it, and its second nodal point should 
coincide with the first nodal point of the eye. The placing of 
the auxiliary lens in front of the cornea alters the position of 
the cardinal points of the combined system, and also alters the 
focal distance of the auxiliary lens. But the actual changes 
in the lens during accommodation are nearly proportional to 

— = — — — , so that the formula serves practically for propor- 
tional magnitudes, ?'. c, for comparing reciprocally the different 
values of the range of accommodation under different circum- 
stances. 



484 



THE OUTGO OF ENERGY 



other words, a convex lens of 5 D must be placed 
before the cornea in order to enable the eye with 
ciliary muscle relaxed to see clearly an object 
situated at the near point. 

The near point recedes as the lens becomes 
harder with advancing age until about the seven- 
tieth year, when R = infinity, and accommodation 
is lost. 

RANGE OF ACCOMMODATION AT DIFFERENT 
AGES 



Age 


P 


P 


in years. 


in dioptres. 


in cm. 


15 


12.0 


8.3 


25 


8.5 


12 


35 


5.5 


18 


45 


3.5 


28 


55 


1.75 


55 


65 


0.75 


133 


70 





00 



Ophthalmoscopy 

Reflection from Retina. — 1. Copy the construc- 
tion used to find the image of the point i formed 
by the dioptric system C (page 457). Assume 
that the image is itself luminous, and that rays 



REFRACTION IN THE EYE 485 

in the last medium are passing from the image 
to the second (now the first) refracting surface. 
Find the point at which these rays unite in the 
first medium (now the second). 

The rays will unite at the original luminous 
point. If the eye be accommodated for a light 
placed in front of it, an image of the light will 
be formed upon the retina. A portion of the 
light rays entering the eye will be reflected from 
this image. Passing back over their original course, 
they will form in turn an image which will ex- 
actly coincide with the luminous object. 

2. Draw a horizontal line as a visual axis. 
Upon this visual axis draw two reduced eyes, 
normal size (Fig. 65), facing each other a conven- 
ient distance apart (5 cm.). Let the left be the 
observer's eye, and the right the eye of the sub- 
ject. On the visual axis behind the observer's 
eye draw a lamp flame. Assume that the sub- 
ject's eye is accommodated for this flame. 

The construction shows that were the observ- 
er's eye away, an image of the flame would be 
formed on the retina of the subject's eye. The 
image would reflect light toward the flame. This 
reflected light would enter by the observer's 
eye, and the illuminated area of the subject's 
retina thus be made visible, were it not that the 
observer's eye is necessarily placed in the visual 



486 THE OUTGO OF ENERGY 

axis, and thus intercepts the rays from the source 
of light to the subject's eye. The interior of the 
eye is therefore not illuminated, and the pupil 
remains dark. 

3. Three millimetres behind the principal 
point of each of the two reduced eyes draw a 
diaphragm (iris) with an aperture (pupil) four 
millimetres in diameter. Assume that the sub- 
ject's eye is accommodated for the pupil of the 
observer's eye. 

Note that a dark image of the pupil of the ob- 
server's eye will be formed on the retina of the 
subject's eye. The rays reflected from this image 
will form a second dark image which will exactly 
coincide with the pupil of the observer's eye. 
Thus the observer will see only the reflection of 
.his own black pupil in the subject's eye. 

4. Throw light into the subject's pupil from a 
lamp held as near the observer's eye as possible. 
The subject should not look at either the observer 
or the light, and his eye should be accommodated 
for a distance much less or much greater than 
that of the observer or the light. 

Part of the pupil will appear red. It has been 
shown in Constructions 2 and 3 that the pupil or- 
dinarily appears black. When, however, a part of 
the image of the light on the retina of the subject 
coincides with that of the pupil of the observer, 



feEFRACiTiON IN THE EYE 48? 

and when the subject's eye is not accommodated 
for either the light or the observer 's pupil, some 
of the light reflected from the subject's retina will 
reach the retina of the observer (Helmholtz). 

Influence of Angle between Light and Visual 
Axis. — 1. Draw a reduced eye with pupil of 
four millimetres diameter as described above. 
Draw to the margins of the pupil an illuminating 
pencil of parallel rays that shall make with the 
visual axis an angle of about 20°. Draw the 
course of these rays from the pupil to the retina 
(seepage 457). On the opposite side of the visual 
axis mark the nodal point of the observer's eye 
in such a position that the observer's visual axis 
shall make also an angle of about 20° with the 
visual axis of the subject's eye. Draw rays from 
this nodal point to the pupil, and thence to their 
focus on the retina. 

The portion of the interior of the eye visible 
to the observer will be that included between 
the outermost rays of the two conical pencils, the 
common base of which is the pupil. Note that 
the apex of the cone is a short distance behiud 
the nodal point. The visible portion includes 
therefore only a part of the anterior chamber, a 
small portion of the lens, and a very small por- 
tion of the vitreous. 1 

1 This matter is clearly presented by Dr. John Green in his 



488 THE OUTGO OF ENERGY 

2. Eepeat Construction 1, but bring the light 
nearer the observer's eye. 

Diminishing the angle between the axis of the 
observer's eye and the axis of the illuminating 
pencil increases the length of the cone formed by 
the intersection of the illuminating pencil and 
the pencil to the observer's eye. Thus the ob- 
server sees a larger cross-section of the lens and 
vitreous, and sees farther into the eye. 

3. Eepeat Construction 1, but place the ob- 
server's nodal point in the axis of the illuminat- 
ing pencil. 

The point of the cone will reach the retina. 
The light reflected will emerge from the emme- 
tropic eye in parallel rays which will enter the 
observer's eye and form upon his retina an image 
of the illuminated area of the subject's retina. 

Influence of Size of Pupil. — Eepeat Construc- 
tion 1 of the preceding section, but enlarge the 
diameter of the pupil to eight millimetres. 

The visible portion of the interior of the eye is 
greater with a large pupil than with a small one. 

Influence of Nearness to Pupil. — Eepeat Con- 
struction 1, but draw the observer's eye nearer the 
subject's eye. 

Note that rays from a larger portion of the 

article on tlie Ophthalmoscope printed in the first edition of 
Wood's Reference Handbook of the Medical Sciences. 



REFRACTION IN THE EYE 489 

subject's retina enter the pupil of the observer 
when the eyes are near. 

Ophthalmoscope. — 1. The eye of the observer 
cannot be placed in the axis of the illuminating 
pencil without shutting off the illuminating rays. 
This difficulty was obviated by the invention of 
the ophthalmoscope. 

Place the electric lamp at the same height as 
the artificial eye, and a little in front of and to 
one side of it, so that the axis of the illuminating 
pencil shall be at right angles with the visual 
axis of the artificial eye. In front of the artificial 
eye set a clear glass plate at an angle of 45° to 
the axis of the illuminating pencil. A portion 
of the rays which fall upon this plate will pass 
through the transparent glass and be lost. An- 
other portion will be regularly reflected, and will 
be thrown into the artificial eye. A portion of 
the light returning from the interior of the ob- 
served eye will be reflected by the glass plate 
and lost. Another portion will be transmitted 
through the glass plate in the direction of the 
visual axis of the observed eye, and may be 
received by the eye of an observer placed in this 
axis, as shown in the preceding construction 
(Helmholtz). 

2. Examine the Loring ophthalmoscope. Its 
essential parts are (1) the mirror of concave 



490 THE OUTGO OF ENERGY 

glass, silvered, pierced at its middle point with 
an aperture of about 2.5 mm., pivoted to turn to 
either side ; (2) two rotating disks carrying a 
series of concave and convex lenses in front of 
the aperture. 

The silvered mirror reflects more light than 
the mirror of transparent glass. Further, it 
allows the lamp to be placed at the side of the eye 
to be examined, and at any required distance from 
the mirror. The turning of the mirror upon a 
pivot permits the more or less oblique incident 
rays to be thrown into the eye without tilting 
the disks carrying the lenses, and thus rendering 
the lenses astigmatic by placing them at an 
angle to the optical axis which passes from the 
subject's retina through the aperture of the mir- 
ror and through the lens behind the aperture 
into the observer's eye. 

The disks may be used singly or in combi- 
nation. A series of concave lenses (marked — ) 
from 1 D to 24 D, and a series of convex lenses 
(marked +) from 1 D to 23 D, are thus secured. 

Direct Method 

Emmetropia. — 1. Eemove from the lantern 
the tubes holding the projecting lens. Place the 
ground glass screen before the condenser. See 



REFRACTION IN THE EYE 491 

that the inner tube of the artificial eye is drawn 
out to the line marked zero upon its scale ; the 
eye is then accommodated for distant vision. Set 
the eye at the level of the observer's eye and 
near the edge of the table. Place the light on the 
right side of the artificial eye and slightly behind 
it. Hold the ophthalmoscope in the right hand 
close to' the right eye at a distance of about fifty 
centimetres from the artificial eye, and look 
through the aperture in the mirror. The elbow 
should be close to the side. The head should 
be vertical so that the observer's eye and the 
artificial eye may have the same visual axis. 
Keep the reflected light upon the pupil of the 
artificial eye. It will be illuminated by the red 
reflection from the choroid coat. With the pupil 
illuminated, approach the artificial eye until the 
lens-bearing disk lies in the anterior principal 
focus (50 mm. in front of this eye, 13 mm. in 
front of the cornea of the normal human eye; 
see page 494.) The artificial eye is accommodated 
for distant objects. The observer's eye must also 
be accommodated for distant vision. The power 
of voluntarily relaxing the ciliary muscle is at- 
tained by practice ; the observer should endeavor 
to look through and beyond the eye at some dis- 
tant object. If the observer be myopic or hyper- 
metropic, his refractive error should be corrected 



492 THE OUTGO OF ENERGY 

by placing the appropriate lens before the opening 
in the mirror. 

As the eye is approached, the details of the 
fundus will come into view. Find the optic disk. 
Trace the branches of the central artery and vein 
which perforate the disk. The image of these 
parts is virtual, magnified about sixteen times, 
and erect. 

2. Copy Construction 2, page 485, in which 
two reduced eyes are placed on the same visual 
axis facing each other. At the anterior prin- 
cipal focus of the subject's eye draw a concave 
mirror of 175 mm. focal distance with an aper- 
ture of 2.5 mm. through which passes the visual 
axis. 

The rays converging from the mirror and pass- 
ing through the pupil are still further converged, 
and are brought to a focus in the vitreous, 
whence they diverge to fall in dispersion circles 
upon the retina, a large area of which is thus 
illuminated. 

Draw rays reflected from the retina to the 
pupil of the subject's eye. They must emerge 
from the eye parallel. Entering the observer's 
eye, with accommodation relaxed, they will be 
brought to a focus on the retina. Show by a 
construction that the image of the optic disk 
formed in the observer's eye will be inverted but 



REFRACTION IN THE EYE 493 

will appear to be upright and of its natural size 

(1.5 mm.). 

The apparent size of this image depends upon 

a visual judgment. The observer knows that 

small objects are usually held about 250 mm. in 

front of the nodal point. The size of an object 

which at this distance would give a retinal image 

1.5 mm. in diameter, can be found by formula 5, 

page 465. 

B : 1.5 :: 250 : 15 

B = 25 mm., the apparent size of the optic 
disk viewed by the direct method. 

Ametropia; Qualitative Determination. — 1. 
Let an assistant make the artificial eye ametropic 
by moving the draw-tube until the optical axis is 
shorter or longer than normal. The observer 
should not know which form of ametropia has 
been produced. Examine the retina with the 
ophthalmoscope held from 30 to 50 cm. in front 
of the artificial eye. 

If the details of the fundus can be seen, the 
eye is either myopic or hypermetropic. 

Move the head with the ophthalmoscope from 
side to side. 

If the vessels appear to move in the same 
direction, the eye is hypermetropic; if in the 
opposite direction, the eye is myopic. 

Measurement of Myopia. — The accomnioda- 



494 THE OUTGO OF ENERGY 

tion of the observer's eye and the eye to be ex- 
amined should be relaxed. The observer's eye 
must be emmetropic ; if it be myopic or hyper- 
metropic, the defect should be corrected by the 
proper glass before the subject's myopia can be 
measured. The correction may be made with 
spectacles, or with one of the lenses in the disk 
of the ophthalmoscope. The ophthalmoscope 
should be placed in the anterior focal plane of 
the eye examined (13 mm. in front of the cornea 
of the human eye, 50 mm. in front of the artifi- 
cial eye). If the observer cannot reach this 
point, in examining the human eye, the distance 
between the correcting lens and the anterior 
principal focus must be subtracted from the 
focal distance of the correcting lens in order to 
find the degree of hypermetropia, and be added 
to the focal distance of the correcting lens in 
order to find the degree of myopia. Viewed 
from the anterior principal focus, the fundus will 
be blurred. 

If myopia be present, turn the disk until that 
concave lens is found which will render clear the 
image of some one of the vessels * near the border 
of the optic disk. The rays emerging from the 
myopic eye are convergent. This lens makes 

1 The error introduced by neglecting the distance between the 
vessels and the nerve elements of the retina-is inconsiderable. 



REFRACTION IN THE EYE 495 

them parallel, and its focal power is the measure 
of the myopia. 

Measurement of Hypermetropia. — If the image 
of the fundus be blurred by hypermetropia, place 
convex lenses before the eye until the strongest 
convex lens is found through which the observer 
can see clearly the retinal vessel or other point 
selected. The rays emerging from the hyperme- 
tropic eye are divergent. This lens renders 
them parallel, and its focal power is the measure 
of the hypermetropia. 

Measurement of Astigmatism. — Set the retinal 
tube of the artificial eye at zero. The eye is now 
emmetropic. Place before the eye the cylindrical 
lens of. + 2D. Examine the fundus with the 
ophthalmoscope. The observer's accommodation 
must be relaxed. 

The optic disk will no longer appear circular, 
but will be elongated in the direction of the 
meridian of greatest curvature. The retinal ves- 
sels will not all be in focus. If a horizontal ves- 
sel be seen distinctly, and the vertical vessel at 
right angles to it is blurred, the eye is astigmatic 
in the horizontal meridian (compare page 423, and 
remember that the breadth of the image of the 
vessel is determined by means of the rays passing 
through that meridian of the cornea which lies at 
right angles to the vessel's course.) With the aid 



496 THE OUTGO OF ENERGY 

of the graduated circle on the front of the artifi- 
cial eye determine the meridian in which the eye 
is astigmatic. Find the lens which will make the 
blurred vessel distinct. If the lens, for example, 
have a focal power of + 2 D, there is simple hyper- 
metropic astigmatism of + 2 D in the given 
meridian. If a lens of — 2 D be required, there 
is simple myopic astigmatism of — 2 D in the 
given meridian. 

In compound astigmatism, the eye is asymmet- 
rical in more than one meridian. Thus a clear 
image of the vertical vessels may be obtained 
with a convex lens of + 2 D, while the horizontal 
vessels may require a lens of -f 1 D. 

The ophthalmoscopic measurement of astigma- 
tism in the human eye is exceedingly difficult, 
and should always be corrected by more reliable 
methods. 

Indirect Method 

1. Arrange the light and the artificial eye as 
directed for the examination by the direct 
method. Hold the ophthalmoscope 30 cm. from 
the artificial eye. With the other hand hold a 
convex lens of 20 D at its own focal length of 
50 mm. in front of the cornea. The rays return- 
ing from the fundus pass through this lens and 
form an image in the air between the observer 



REFRACTION IN THE EYE 497 

and the lens. Examine this image through a 
magnifying glass of + 5 D placed behind the 
aperture of the mirror. If the observer be 
myopic in moderate degree, the aerial image will 
lie near his far point, and he will need no mag- 
nifying or correcting glass; if the myopia be 
excessive, a weak concave glass should be used. 
If the observer be hypermetropic, the degree of 
his hypermetropia should be added to the focal 
distance of the magnifying glass. The confusing 
bright reflexes from the surfaces of the 20 D lens 
may be avoided by holding the lens slightly 
oblique to the optical axis. 

The subject's eye and the 20 D lens form a 
refracting system like the objective of the com- 
pound microscope; the ophthalmoscopic lens 
plays the part of the ocular. 

The image is real, inverted, and magnified. 
But it will appear to be upright. In it all the 
relations of the retinal objects are reversed. If 
the observer move, the image will move in the 
opposite direction. The size of the image is found 
by formula 5, p. 61. B is the size of the aerial 
image, b the size of the optic disk = 1.5 mm., g 1 
the focal distance of the 20 D lens = 50 mm., </, 
the distance from the nodal point to the retina 
= 15 mm. Then 

B : 1.5 : : 50 : 15, and B = 5 mm. 

32 



498 THE OUTGO OF ENERGY 

Thus the enlargement of the retinal details is 
less than with the direct method. When the 
aerial image is viewed through the ophthalmo- 
scopic lens of + 5 D, an enlarged virtual image 
of the first image is formed, as in the microscope. 
2. Draw constructions showing the formation 
of the image in the direct and indirect methods. 
Eemember that in the indirect method the rays 
from the mirror come to a focus before reaching 
the convex lens. Their second focus is in the 
vitreous. 



vision 499 



X 



VISION 

Mapping the Blind Spot. — Fasten a rod fifteen 
inches from the table. Beneath the rod place 
a well-lighted sheet of white paper (a page of 
the laboratory note-book will serve). Make a 
small black cross near the left margin. Eest 
the chin upon the rod in such a way that the 
right eye shall look directly down at the cross. 
Place the hand over the other eye. A straw 
bearing a black pin-head will be drawn by an 
assistant from the cross along the horizontal 
meridian toward the temporal side of the eye 
under observation. The assistant will mark the 
point where the black object ceases to be visible, 
and the point at which it reappears. These are 
the boundaries of the blind spot of the right 
eye in the horizontal meridian. Determine the 
boundaries in other meridians. Obtain similarly 
the outlines of the blind spot of the left eye. 

Yellow Spot. — Close the eyes for half a 
minute, and then look at the clear sky or a 
brightly lighted surface through a solution of 
chrome alum in a glass bottle with parallel 
sides. The yellow spot will appear rose-colored 



500 THE OUTGO OF ENEEGY 

in the blue-green-red solution. The yellow pig- 
ment absorbs some of the blue and green rays. 
The remaining rays form rose color. 

Field of Vision. — Fasten in a vertical position 
a sheet of white paper about 50 cm. high and 
60 cm. broad. (It may be pinned to the wooden 
stand set on edge upon the electrometer box.) 
About 20 cm. from the left margin and 30 cm. 
from the lower margin of the paper mark a small 
cross. Let the subject rest his chin upon a rod 
clamped to the iron stand in such a way that 
the right eye shall look directly at the cross. 
Cement the squares of black, red, green, and 
blue papers to the ends of separate straws. 
Carry the black square from without inwards 
along the horizontal meridian intersecting the 
cross. Mark the point at which the black 
object enters the field of vision. This point is 
the temporal boundary of the visual field in the 
horizontal meridian. Determine in the same 
way the boundary on the nasal side. Eepeat 
for several other meridians. A line joining the 
points obtained will bound the visual field. 

Determine the visual field for red, green, and 
blue. Always pass the test color from without 
inwards. The subject should be ignorant of 
the color to be used, and should name the color 
as soon as it enters his visual field. 



VISION 501 



Color Blindness 

The three large skeins show the test colors. 

1. Light Green. — Palest (lightest) shade of 
very pure green, — neither yellow-green nor 
blue-green to the normal eye. Light green is 
chosen because, according to the Young-Helm- 
holtz theory, it is the whitest of the colors of 
the spectrum, and, consequently, is most easily 
confused with gray. Light shades are employed 
because it is difficult to distinguish between 
strongly illuminated shades. 

2. Purple (Rose). — A skein midway between 
lightest and darkest purple. Chosen because 
purple combines two fundamental colors which 
are normally never confounded. 

3. Red. — A vivid, slightly yellowish red. 
Chosen because it represents the color-group in 
which red (orange) and violet (blue) are com- 
bined in nearly equal proportions. 

Method of Examination and Diagnosis. — Place 
the Berlin worsteds on the white cloth in which 
they are wrapped. They should be well mixed, 
and not spread out too much. Lay a skein of 
the first test-color in a well-lighted position two 
or three feet from the group. Inform the person 
examined : 



502 THE OUTGO OF ENERGY 

(1) That he must not speak during the test. 

(2) That the skeins are not to he fingered or 
tossed about. A skein should be touched only 
after its selection. 

(3) That he must endeavor to pick out skeins 
resembling the test skein, i. e., a little lighter or 
darker in shade ; the resemblance cannot be per- 
fect, as no two shades are exactly alike. 

Green Test. — The subject must pick out all 
the other skeins approximately the same shade. 

The color-blind selects some shade of gray. 

Purple {Rose). — The subject should pick out 
the skeins of the same color, as before. 

(1) He who is color-blind by the first test, and 
who, upon the second test, selects only purple 
skeins, is incompletely purple-blind. 

(2) He who, in the second test, selects with 
purple only blue and violet, or one of them, is 
completely red-blind. 

(3) He who, in the second test, selects with 
purple only green and gray, or one of them, is 
completely green-bli?id. 

Remark. — The red-blind never selects the 
colors taken by the green-blind, and vice versa. 
Often the green-blind places a violet or blue 
skein by the side of the green, but only the 
brightest shades of these colors. This does not 
influence the diagnosis. 



vision 503 

Bed. — This test is applied to those completely 
color-blind. Continue the test until the person 
examined has placed beside the specimen all the 
skeins belonging to this shade, or else, separately, 
one or more " colors of confusion." 

The red-blind chooses (besides the red, green, 
and brown) shades which to the normal sense 
seem darker than red. The green-blind selects 
opposite shades, which seem lighter than red. 

Violet Blindness. — Very rare. Recognized by 
a confusion of. purple, red, and orange, in the 
purple test (see 2). Much care is required to 
diagnosticate this form. 

The Respiration Scheme. 1 — The glass cylinder 
(Fig. 67) represents the thorax. The surface of the 
water in the glass cylinder represents the diaphragm 
and movable chest walls ; its level may be changed 
by raising or lowering the large rubber tube, in the 
free end of which is placed a second glass cylinder, 
not shown in Fig. 67. The interior of the cylinder 
above the water represents the thoracic cavity, and 
the rubber balloon the lungs. The paraffined cork 
is pierced by a pleural and a tracheal tube. The 
upper end of the pleural tube enters a rubber tube, 
in the wall of which is a small hole closed by a short 
glass rod. Through this hole the pleural cavity may 
be opened to the atmospheric air. The tracheal tube 

1 American Journal of Physiology, 1904, x, p. xlii. 



504 



THE OUTGO OF ENERGY 



opens below into the lung, above into a rubber tube 
in the wall of which is a small opening, which repre- 
sents the glottis, and which may be partly or wholly 
closed by a glass rod. The left manometer shows the 
intrathoracic pressure, the right manometer the intra- 




Fig. 67. The respiration scheme; about one-third the actual size. 



pulmonary pressure. The normal relations between 
intrathoracic and intrapulmonary respiration may be 
reproduced with this apparatus. The pressure changes 
in forced respiration, obstructed air passages, asphyxia, 
coughing, sneezing, hiccough, and perforation of the 
pleura may also be studied. 



KESPIRATION 505 

XI Mechanics of Kespiration 

Artificial Scheme. — Eaise the left glass rod 
above the opening in the rubber tubing (Fig. 67). 
Hold the lower end of the free cylinder even with 
the rubber balloon, and pour in water till the 
level just readies the balloon. Lower the left 
glass rod to cover the opening. 

The surface of the water in the attached 
cylinder represents the diaphragm and movable 
chest-walls ; the interior of the cylinder above 
the water, the thoracic cavity ; and the rubber 
balloon, the lungs. The left manometer shows 
the intra- thoracic pressure ; the right manometer 
shows the intra-pulmonary pressure. The left 
glass rod closes the entrance to the cylinder, 
i. e. makes the thoracic cavity a closed cavity, 
as is normal ; the right glass rod, with its lower 
end partly covering the opening in the rubber 
tubing, controls the entrance to the balloon (the 
respiratory passages). 

Inspiration. — Nearly close the respiratory pas- 
sage. Lower the water level to the base of the 
thoracic cylinder. 

Note the change in the size of the lung, and 
in the pressure in the lung and in the thorax. 
G-ive reasons for these changes. 

Expiration. — Widen the respiratory passage 



506 THE OUTGO OF ENERGY 

slightly. Eaise the water level slowly till the 
lung is slightly but evenly distended. 

Note the pressure in the pleural cavity. Is it 
positive or negative ? Why ? 

Normal Respiration. — Slowly and rhythmi- 
cally raise and lower the diaphragm (water level) 
between the inspiratory and expiratory level, 
taking care that the lung never becomes even 
slightly collapsed at the end of expiration. 

Give reasons for the changes in the intra- 
pulmonary pressure. 

Forced Respiration. — Eaise and lower the 
diaphragm more quickly. 

Observe that the differences in pressure are 
increased. 

Obstructed Air Passages. — Diminish the inlet 
in the respiratory tube by moving the glass plug. 
Raise and lower the diaphragm. 

The differences of pressure will be increased. 

Asphyxia. — Close the entrance to the lungs 
entirely. 

Note the effect of movements of the diaphragm 
upon the intra-thoracic and intra-pulmonary 
pressures. 

Coughing : Sneezing. — Remove the glass rod 
from the respiratory passage. Bring the lung to 
full inspiration. Close the respiratory opening 
with the moistened thumb. Raise the diaphragm 



RESPIRATION 507 

half-way toward expiration. Suddenly open the 
respiratory passage. 

Air is quickly and forcibly expelled from the 
lung (cough, sneeze). 

Hiccough. — Lower the diaphragm quickly 
toward full inspiration, and while the lung is 
expanding close the respiratory opening with 
the moistened thumb (hiccough). 

Note the sudden changes of pressure in the 
two cavities. 

Perforation of the Pleura. — Open the inlet to 
the pleura. 

Note the effect of the opening into the pleural 
cavity upon the lung and upon the intra-pulmo- 
nary and intra-thoracic pressure. 

Observe the result of movements of the 
diaphragm. 



508 THE OUTGO OF ENERGY 

XII 

THE CIRCULATION OF THE BLOOD 

The Mechanics of the Cieculation 

The spaces between the cells of which the body 
is composed are filled with a liquid called the 
lymph, from which the cells take their food and 
into which they pour their waste. The materials 
and the products of metabolism diffuse from 
lymph to cell and from cell to lymph. In 
animals in which the division of labor has 
produced separate organs for digestion, excre- 
tion, and the like, the lymph serves as a medium 
of exchange. For this purpose the relatively 
slow processes of diffusion are not sufficient. 
Food must be more rapidly brought and waste 
more rapidly removed. A circulation must be 
provided. There are many ways in which the 
necessary circulation is secured. In Cyclops a 
flow is caused by movements of the alimentary 
canal. In Daphnia, the lymph enters a hollow 
muscle and is then expelled. In the higher 
animals the provision for rapid exchange is two- 
fold. The intercellular spaces are traversed by a 



THE CIRCULATION OF THE BLOOD 509 

countless number of tubes of capillary size, the 
walls of which are so thin that substances in 
solution pass through them with great ease. 
These capillaries are the ultimate branches of 
a single tube, and, after fulfilling their function, 
the capillaries unite into a single tube again. A 
closed system is thus formed. This system is 
filled with a modified lymph called the blood, 
which is kept in constant circulation Thus the 
lymph in the intervascular spaces is in intimate 
contact with a continually changing liquid. 
Further provision for rapid exchange is found 
in the circulation of the lymph itself. The 
spaces between the cells are drained by channels 
which gradually become definite tubes, the lym- 
phatics, and these finally join to form two ducts 
which empty into the blood vessels. 

The unbranched portion of the vascular tube 
is dilated into a cavity with thickened muscular 
walls termed the ventricle of the heart. The 
ventricle contracts rhythmically. Each contrac- 
tion raises the pressure in the ventricle until it is 
higher than the pressure in the remaining blood 
vessels. The blood in the ventricle is thereby 
forced into the blood vessels against the resist- 
ance of friction. The high pressure in the ven- 
tricle during contraction is transmitted into the 
blood vessels and through them. At each cross- 



510 THE OUTGO OF ENEKGY 

section of the vascular system some of the pres- 
sure is lost in overcoming resistance ; hence the 
pressure gradually falls. The blood flows from 
the area of higher pressure, near the ventricle, to 
the area of lower pressure. Thus the contrac- 
tions of the ventricle establish a difference of 
pressure in the blood vessels, which causes a 
movement of the contained liquid. 

At the two points at which the vascular 
tube joins the ventricle membranous valves are 
placed. One of these valves opens into the 
ventricle. It is an inflow valve. The inflow 
valve closes when the ventricle contracts. Con- 
sequently the contractions cannot drive the 
blood through this orifice. The ventricle can 
drive the blood only through the remaining 
orifice. Thus the ventricle becomes a pump 
and its contractions move the blood always 
in one direction. The vessels by which the 
blood is carried from the ventricle to the cap- 
illaries are called arteries ; those which bring 
the blood from the capillaries back to the ven- 
tricle are called veins. Adjoining the ventricle 
the great veins meet in a common enlarge- 
ment called the auricle. It is at the junction of 
the auricle with the ventricle that the inflow 
valve is placed. 

The outflow valve is placed at that orifice of 



THE CIRCULATION OF THE BLOOD 511 

the ventricle which opens into the arteries. 
When the ventricle, having by its contraction 
raised the pressure in the arteries, begins to 
relax, the pressure within its cavity becomes less 
than that in the arteries. The outflow valve 
then shuts. Otherwise the arteries would be 
placed in direct communication with an area of 
low pressure and the relaxation of the ventricle 
would undo in part the work of the contraction, 
the purpose of which was the creation of a pres- 
sure in the arteries great enough to force the 
blood through all the blood vessels. 

It is obvious from these general considerations 
that the problems of the circulation are in the 
first instance those presented by any system of 
closed tubes through which liquid is driven by a 
pump. 

The Circulation Scheme. 1 — The artificial scheme 
(Fig. 68) to illustrate the mechanics of the circulation 
in the highest vertebrates consists of a pump, a sys- 
tem of elastic tubes, and a peripheral resistance. The 
inlet and the outlet tubes of the pump are furnished 
with valves that permit a flow in one direction only. 
The peripheral resistance is the friction which the 
liquid undergoes in flowing through the minute chan- 
nels of a piece of bamboo. To this must be added 

1 Science, 1905, xxi, pp. 752-754. 



512 



THE OUTGO OF ENERGY 



the slighter resistance due to friction in the rubber 
and glass tubes. 

In this system the pump represents the left ven- 
tricle ; the valves in the inlet and outlet tubes, the 




Fiy. 6S. Quantitative circulation scheme ; about one-fourth the actual 
size. 

mitral and aortic valves, respectively ; the resistance 
of the channels in the bamboo, the resistance of the 
small arteries and capillaries. The tubes between 
the pump and the resistance are the arteries ; those 
on the distal side of the resistance are the veins. 



THE CIRCULATION OF THE BLOOD 513 

The side branch substitutes a wide channel for the 
narrow ones, and thus is equivalent to a dilatation of 
the vessels. # 

The pressure in the ventricle is varied through a 
tambour covered with rubber membrane. The mem- 
brane is grasped between two disks, one below and 
one above. The upper disk is screwed down upon 
the lower until the membrane is tightly held. To 
these disks is fastened a rod which ends in a yoke. 
The yoke rests upon a small wheel, which in turn is 
supported by a brass plate eccentric in form. This 
brass plate is revolved by turning a handle attached 
to the axle. As the plate revolves the small wheel 
bears upon the eccentric rim and rises and falls with 
the rise and fall in the rim of the plate. The motion 
of the small wheel is transferred through the yoke, 
rod, and disk to the rubber membrane, and thus to the 
interior of the ventricle. 

The rim of the eccentric brass plate reproduces the 
intraventricular pressure curve in the dog. In pro- 
jecting this curve upon the plate the periphery is 
divided into fractions of a second, and the radii are 
divided into millimetres of mercury pressure. 

Each revolution of the eccentric plate reproduces in 
the ventricular tube both the time and the pressure 
relations of the ventricular cycle in the dog. The 
intraventricular pressure curve may be written by 
connecting the side tube with a membrane manometer, 
and clamping off the arterial mercury manometer to 
be mentioned shortly. 

33 



514 THE OUTGO OF ENERGY 

When the pressure rises in the ventricle to a suffi- 
cient height the contents of the ventricle will be dis- 
charged through the aortic valve into the aorta, and 
thus (through a convenient metal tube) into the 
arterial tube, leading to the capillary resistance. 
Here two paths may be taken : the liquid may pass 
either through the capillary channels in the cane, thus 
meeting with a high resistance, or this resistance may 
be lessened to any desired degree by unscrewing a 
clamp and thus opening the side tube. Both paths 
lead to the venous tubes, whence the liquid passes 
through the mitral valve into the ventricle. The 
mitral and aortic valves are of a modified Williams 
type. Metal tubes closed at one end conduct the 
liquid respectively to or from the ventricle. The 
liquid enters or leaves the valve-tube through a 
hole covered by a rubber valve-flap, not shown in 
Fig. 68. Each valve is surrounded by a glass tube 
through which the working of the valve may be 
inspected. 

Mercury manometers measure the pressure in the 
arteries and veins near the capillary resistance. The 
arterial manometer is provided with a glass thistle- 
tube to catch any mercury that may be driven out by 
a careless operator. 

If the arterial mercury manometer be replaced by a 
membrane manometer, or if it be provided with a float 
and writing point arterial-pressure curves may be writ- 
ten, identical with those obtained from the carotid 
artery of the dog. 



THE CIRCULATION OF THE BLOOD 515 

Normal sphygmographic tracings may be obtained 
by using a sphygmograph on the aortic tube. 

Palpation of the arterial tube will give a pulse the 
"feel" of which cannot be distinguished from that of 
the pulse in the normal subject ; the pressure waves 
in the quantitative scheme and in the living animal 
are identical in respect of both time and pressure. 

The Conversion of the Intermittent into a 
Continuous Flow 

When a pump forces water or any other 
incompressible fluid through tubes with rigid 
walls, the inflow and outflow are equal and in the 
same time. The outflow ceases the instant the 
inflow ceases. The same is true in a system of 
elastic tubes so short and wide that friction be- 
tween the liquid and the walls causes practically 
no resistance to the flow. Here the quantity 
received from the pump can still escape from the 
distal end of the system during the stroke of the 
pump. When the resistance is increased by 
narrowing the tubes, or by increasing their 
length, or in both these ways, not all the liquid 
received from the pump can pass by the resist- 
ance during the stroke of the pump, — the re- 
mainder must pass during the interval between 
one stroke and the next. The portion which 
cannot pass during the stroke finds room be- 



516 THE OUTGO OF ENEKGY 

tween the pump and the resistance in the dilata- 
tion of the containing vessels. To effect the 
dilatation the force or pressure transmitted from 
the pump presses out the vessel walls until this 
pressure is held in equilibrium by the elastic re- 
action of the walls. As the pressure from the 
pump wanes, the energy stored by it in the ten- 
sion of the vessel walls is reconverted into 
mechanical motion, and the walls return towards 
their original position, driving the liquid out of 
the tube past the resistance. 

1. Open the side branch by unscrewing the 
pressure-clip. See that the tubes are well filled 
with water. Make a single brief gentle pressure 
on the ventricle. 

Note (1) that practically ail the liquid driven 
out by the stroke escapes through the side 
branch, in which the resistance is low, rather 
than through the high capillary resistance. 
(2) Only a portion of the liquid escapes during 
the stroke. (3) The portion which cannot 
escape by the resistance during the stroke finds 
space in a very evident dilatation of the tubes 
nearer the pump, i. e. between the pump and 
the principal resistance. (4) A membrane ma- 
nometer coupled to the side tube of the ventricle 
would show a sudden rise and fall indicating 
a sudden rise and fall in the intraventricular 
pressure. (5) Close observation shows that on 



THE CIRCULATION OF THE BLOOD 51 1 

the stroke of the pump the tubing just distal to 
the aortic valve begins to expand sooner than 
that farther away. Evidently the change of 
pressure produced by the stroke of the pump is 
transmitted from point to point through the 
liquid in the tubes. (6) The arterial manometer 
shows a sudden rise and fall. Observe that the 
rise is not synchronous with the stroke of the 
pump, but begins an instant later. This interval 
is occupied by the transmission of the pressure 
change from the pump to the mercury column, 
and in part by the time required to overcome the 
inertia of position of the mercury. The oscilla- 
tions of the mercury following the primary rise 
and fall are due to inertia. (7) Observe the action 
of the valves (they consist of a metal tube, closed 
at one end, and pierced with a hole which is 
covered with a rubber flap tied on both sides of 
the hole). (8) Place a finger on the "aorta" 
near the valve and note the pressure wave (pulse) 
as it passes along the vessel. 

2. With the side branch open as in Experiment 
1, compress the bulb rhythmically and gradually 
increase the frequency of stroke. 

It will be found that at about twenty strokes 
to the minute the stream will be intermittent. 
As the interval between the strokes is shortened 
the liquid received from the pump in any one 



ol8 THE OUTGO OF ENERGY 

stroke cannot all escape by the resistance during 
the stroke and the succeeding interval. The 
next stroke comes before the outflow from the 
preceding stroke is finished, and the stream be- 
comes remittent. 

Still further increase Jbhe frequency of the 
stroke. A rate will be reached at which one- 
half the quantity received from the pump will 
pass by the resistance during the stroke of the 
pump and the remaining half will pass in the 
interval between that stroke and the next ; 
the intermittent will be converted into a con- 
tinuous flow. 

Observe that the duration of the intervals is 
greater than the duration of the strokes of the 
pump. Thus the time during which the circula- 
tion is carried on by the energy stored by the 
pump in the elastic walls of the vessel is greater 
than the time during which it is carried on by 
the direct stroke of the pump. 

Note that the arterial pressure remains low 
even after the stream becomes continuous. An 
increase in the frequency of the beat has little 
influence on the blood pressure where the peri- 
pheral resistance is very slight. 

3. Close the side branch, so that the liquid 
must pass through a high peripheral resistance. 
Compress the bulb at such a rate that the outflow 
shall be continuous. 



THE CIRCULATION OF THE BLOOD 519 

The frequency required to make the flow con- 
tinuous is now much less than when the peri- 
pheral resistance was low. 



The Eelation between Eate of Flow and 
Width of Bed 

In a frog slightly paralyzed with curare destroy 
the brain by pithing, with the least possible loss 
of blood. Lay the frog back down on the mes- 
entery board. Open the abdomen in the median 
line. Draw the intestine over the cover glass 
upon the cork ring so that the mesentery may 
lie upon the glass evenly and without stretch- 
ing. The mesentery must be kept constantly 
moist with normal saline solution. Examine 
the blood vessels in the mesentery with No. 3 
Leitz objective. 

Note the swift flow in the larger vessels and 
the slow movement of the blood through the 
capillaries. 

The combined cross-sections of the capillaries in 
the body are vastly greater than the cross-section 
of the arteries or the veins. The total quantity 
of blood passing in a unit of time through the 
arteries or veins and the capillaries is the same. 
Tf less passed through the capillaries than through 
the arteries, the capillaries would soon be gorged 



520 THE OUTGO OF ENERGY 

to bursting. If more, trie arteries would soon be 
empty. As the quantity passing through the 
capillaries and the arteries and veins in a unit of 
time must thus be the same, it follows that where 
the combined cross-section of the channel or 
" bed " is small, the blood must flow faster than 
where the cross-section is large. A river rushes 
rapidly through a gorge, but moves sluggishly 
where meadow-lands afford a wider channel. 
Thus the blood flows with great velocity in the 
great arteries, less rapidly in their branches, and 
very slowly indeed in the capillaries, the com- 
bined width of which is so great compared to 
that of the arteries. And as the capillaries unite 
into the smaller veins, and these into the larger 
veins, the combined cross-section or bed becomes 
ever smaller and the blood moves ever more 
swiftly. Were the slow passage of the blood in 
the capillaries due simply to friction, the blood 
would move still more slowly in the veins be- 
cause the retarding influence of the friction in 
the veins would be added to that of the capillaries. 
There is an inverse relation between the rate of 
flow and the area of bed. 



the circulation of the blood 521 
The Blood- Pressure 

The Relation of Peripheral Resistance to Blood- 
Pressure. — Eevolve the disk of the artificial 
scheme at a rate that will produce a continuous 
outflow. 

With each successive stroke the portion of 
liquid unable to pass the resistance during the 
stroke and the succeeding interval is added to 
that left behind from preceding strokes. The 
arteries become more and more full. The arte- 
rial manometer registers a higher and higher 
pressure. At length the pressure ceases to rise. 
The mercury remains at a mean level broken by 
a slight accession at each stroke. The pump 
now merely maintains the constant high arterial 
pressure. This pressure suffices to drive through 
the resistance during each stroke and the suc- 
ceeding interval all the liquid received from the 
pump during the stroke. 

The venous pressure remains very low. The 
capillary resistance (to which must especially be 
added the resistance of the smallest arteries) 
almost entirely exhausts the pressure in the 
arteries. Hence the sudden and profound dif- 
ference observed between the arterial and the 
venous pressure. A second arterial manometer 
placed near the aorta would show that the 



522 THE OUTGO OF ENERGY 

loss of pressure between the ventricle and the 
smallest arteries is relatively slight. 

The pulse is absent on the venous side of the 
resistance. 

The Curve of Arterial Pressure in the Frog. — 
Expose the heart of a frog, the brain of which has 
been pithed without haemorrhage. Provide a fine 
cannula w T ith a short piece of rubber tubing. 
Fill cannula and tube with one per cent sodic car- 
bonate solution, and close the end of the tube with 
a small glass rod. Tie a ligature about one aorta 
as far as possible from the junction of the two 
aortas. Knot the ends of the ligature together. 
Pass a second ligature beneath the same aorta, but 
do not tie it. Lift the vessel by the second 
ligature so that the vessel is constricted by lying 
across the thread. Between the two ligatures 
open the aorta with sharp scissors and introduce 
the cannula. Fasten the cannula in place by 
means of the ligature. Place the frog -board on 
the wooden stand to bring the heart on a level 
slightly higher than the level of the mercury in 
the mercury manometer (Fig. 69). See that the 
proximal limb of the manometer is filled with 
one per cent sodic carbonate solution to the ex- 
clusion of air. Bring the writing point of the 
manometer against a smoked drum and revolve 
the drum once by hand to record a line of atmos- 



THE CIRCULATION OF THE BLOOD 



523 



pheric pressure. Close the aorta containing the 
cannula by gentle pressure with a forceps the 
blades of which are covered with rubber tubing. 
Join the cannula-tube to the manometer, exclud- 
ing air bubbles. Eemove the forceps. 

The mercury will fall in the proximal and rise 
in the distal limb until the blood-pressure in the 
aorta is balanced by the column of mercury. 

With each ventricular beat, . 

the column rises a short dis- 
tance above the mean level 
and sinks again. 

Eecord the blood-pressure 
curve on a very slowly 



moving drum. 



To get the 




Fig. 69. The small mercury 
manometer. 



actual pressure in milli- 
metres of mercury multiply 
by two the mean height of 
the curve above the atmos- 
pheric pressure line. 

The Effect on Blood-Pressure of Increasing the 
Peripheral Resistance in the Frog. — The peri- 
pheral resistance may be increased by the nar- 
rowing of the small arteries which follows the 
stimulation of special vaso-constrictor nerve fibres. 
The vaso-constrictor nerves may be stimulated 
directly or reflexly. The latter method is chosen 
here. 



524 THE OUTGO OF ENERGY 

Expose the sciatic nerve. Tie a ligature about 
the nerve near the distal end of the wound, and 
sever the nerve on the distal side of the ligature. 
Stimulate the central end with a tetanizing 
current of moderate strength. 

The afferent impulses set up by the stimula- 
tion proceed to the spinal cord and thence to the 
bulb, where they excite nerve cells which dis- 
charge impulses that cause the smaller arteries 
(and probably the veins) to constrict. This 
narrowing causes the arterial pressure to rise. 

Changes in the Stroke of the Pump ; Inhibition 
of the Ventricle. — While the arterial pressure in 
the artificial scheme is at a good height (120 mm. 
Hg) arrest the ventricular stroke (the ventricle 
in animals may be thus inhibited by stimula- 
tion of the vagus nerve, page 316). 

So soon as the ventricle ceases to beat, the less 
distended arteries will empty themselves through 
the peripheral resistance, and the arterial man- 
ometer will show a continuous fall in blood- 
pressure. 

Eesume the ventricular beats. 

The mercury in the arterial manometer will 
rise in large leaps, corresponding to the ease with 
which the early strokes of the pump distend the 
lax arteries (the inertia of the mercury somewhat 
exaggerates the rise at each stroke). As the 



THE CIRCULATION OF THE BLOOD 525 

blood-pressure rises, however, the excursion of 
the mercury for each ventricular stroke becomes 
less and less, corresponding to the smaller and 
smaller difference between the pressure in the 
arteries and the maximum pressure within the 
ventricle, until at length equilibrium is restored 
between the peripheral resistance and the force 
and frequency of the ventricular beat. 

The Effect of Inhibition of the Heart on the 
Blood-Pressure in the Frog. — Arrange an induc- 
torium for strong tetanizing currents. Insert 
the electromagnetic signal in the primary circuit 
and bring its writing point beneath that of the 
manometer. Eaise the heart gently. Note the 
white " crescent " between the sinus venosus and 
the right auricle. Put the points of the elec- 
trodes on the crescent, and close the circuit 
for a moment. After one or two beats the 
heart will stop. 

Observe the great fall in blood-pressure. 
Cease the stimulation. 

The mercury returns in leaps to its former 
level. 

The Heart as a Pump 

The Opening and Closing of the Valves. — Secure 
a high arterial pressure (120 mm. Kg) in the 
artificial scheme. Now greatly slow each ven- 



526 THE OUTGO OF ENERGY 

tricular beat and at once observe closely the 
action of the valves. 

It will be seen that the mitral valve closes as 
soon as the ventricle begins to contract, but the 
aortic valve does not open until the intraventric- 
ular pressure has risen above that in the aorta. 
Time is required for this rise in the pressure in 
the ventricle. During this period both mitral 
and aortic valves are closed. When the ventri- 
cle begins to relax, the intraventricular pressure 
speedily falls below that in the aorta, and the 
aortic valve shuts, but the intraventricular pres- 
sure normally must fall at least 100 mm. Hg 
farther before it shall be lower than that in the 
auricle. During this fall all the heart valves are 
again closed ; the aortic valves are already shut, 
and the mitral not yet open. 

The Period of Outflow from the Ventricle. — Tie 
a rubber membrane over the smaller thistle-tube 
of the sphygmograph (Fig. 70) and cement a bone 
button in the centre. Connect a membrane ma- 
nometer 2 with the side tube of the ventricle. 
Bring the writing points of the recording tam- 

1 If such a manometer is not at hand, carry a thin wire from 
the yoke of the disk of the circulation scheme to a light muscle 
lever, counterweighted from the pulley or pulled gently upward 
by a rubber band attached to the lever. This lever will record 
the up and down movement of the disk and thus mark the 
beginning of the ventricular stroke. 



THE GIECULATION OF THE BLOOD 



527 



boui and the manometer into the same vertical 
line against a smoked drum. Let the drum re- 
volve at a fast speed. 

Place the button of the receiving tambour on 
the aorta. It will record the aortic pulse and 
the membrane 
manometer will 
record the intra- 
ventricular pres- 
sure. Let the 
ventricle pump 
with the usual 
force and fre- 
quency. When 
the two curves 
have been writ- 
ten stop the 

clockwork and turn back the drum until the 
point of the lever recording the ventricular pres- 
sure lies at the exact beginning of the upstroke 
in the aortic pulse curve. Cause each lever to 
write an ordinate on the stationary drum. These 
ordinates will indicate synchronous points and 
will mark the beginning of the "outflow" period. 

The Sphygmograph Tambour. 1 — This small and 
very sensitive tambour (Fig. 71) is mounted upon a 

1 First Catalogue of Harvard Physiological Apparatus, 1901, 
p. 47. 




Fig. 70. The sphygmograph. 



528 " THE OUTGO OF ENERGY 

hollow tube through which the air waves reach the 
rubber meuibraue. A right-angled piece of alumin- 
ium transmits the motion of the membrane to the 
writing lever. The moving parts are of the lightest 




Fig. 71. The sphygmograph tambour ; about twice 
the actual size. 



construction. The axle of the writing lever is held in 
a yoke, the distance of which from the fulcrum of the 
lever is readily adjustable. The rubber membrane is 
not tied, but is held in place by a removable ring, — 
a time-saving device. 

If a small glass thistle-tube placed over the carotid 
artery be connected with this tambour by a rubber 
tube, preferably with a side branch, admirable pulse 
tracings may be recorded. By covering the thistle- 
tube with a rubber membrane upon which a bone but- 
ton is cemented, sphygmograms may be taken from 
the radial artery or from the tubes of the circulation 
scheme. The same tambour is used with the plethys- 
mograph tube. 



THE CIRCULATION OF THE BLOOD 529 

Now turn the drum until the point of the 
aortic lever lies beneath the notch seen in the 
down stroke of the pulse curve (the dicrotic 
notch, see page 546). Describe synchronous 
ordinates. It is known that the dicrotic notch 
in the aortic pulse curve corresponds closely to 
the moment of closure of the aortic valves. It 
marks, therefore, the end of the outflow period. 
Note that this . point is reached soon after the 
ventricle begins to relax. Thus the period dur- 
ing which the intraventricular pressure is higher 
than the pressure in the aorta embraces part of 
the relaxation as well as part of the contraction 
of the ventricle. It includes approximately the 
highest third of the intraventricular pressure 
curve. 

Observe also the considerable interval between 
the beginning of ventricular contraction and the 
opening of the aortic valve, as shown by the 
upstroke in the pulse curve consequent upon 
the entrance of liquid into the aorta. 

The Visible Change in Form. — Expose the heart 
of a frog. Observe the great veins, the auricles, 
the single ventricle, the two aorta?, and the dila- 
tation, or bulbus, by which the aortai are con- 
nected with the ventricle. All these parts except 
the two aortas are contracting. The veins con- 
tract first ; the auricles next ; then the ventricle ,* 

34 



530 THE OUTGO OF ENERGY 

last the bulbus. Note the pallor of the contracted, 
empty ventricle. 

Graphic Record of Ventricular Contraction. — 

Pass a fine wire through the tip of the ventricle 
and fasten the free end to the heart lever (Fig. 53). 
Let the lever write on a slow-moving drum. 
Note the characteristics of the curve. 



The Heart Muscle 

All Contractions Maximal. — Inhibit the heart 
by a Stannius ligature (see page 562). Find the 
least strength of stimulus that will cause the ven- 
tricle to contract. Increase the strength of the 
stimulus, but do not stimulate oftener than once 
in ten seconds (to avoid the staircase contractions 
described below). 

The force of ventricular contraction will re- 
main the same, notwithstanding the increased 
stimulus. 

If the heart responds at all to a stimulus, it 
responds by a maximum contraction. There is 
no interval between the minimal and maximal 
value (compare page 175). 

Staircase Contractions. — Find the least stimu- 
lus that will cause the ventricle to contract. 



THE CIRCULATION OF THE BLOOD 531 

Eepeat this minimal stimulus every 5 seconds, 
recording the contractions on a drum turned 
about 5 mm. by hand after each contraction. 

The contractions of the ventricle will be suc- 
cessively stronger, so that the apices of the curves 
will form an ascending line (" staircase "). The 
form of the staircase is always an hyperbola. 
Successively stronger responses to repeated stim- 
uli of uniform strength can also be obtained 
from the curarized gastrocnemius of the frog, 
perfused with blood, and from mammalian and 
invertebrate muscles. The contraction appears to 
increase the irritability. Thus the same stimu- 
lus causes a greater contraction after a brief 
tetanus than before. Rossbach and Bohr have 
observed this after-effect continuing more than 
thirty minutes. 

The Isolated Apex ; Bernstein's Experiment. — 
Draw a ligature about the ventricle halfway be- 
tween base and apex tightly enough to crush the 
tissues without wholly separating them. The 
anatomical continuity between the two halves 
of the ventricle will thereby be maintained, but 
the physiological continuity will be lost. Release 
the ligature. 

The isolated "apex" as a rule does not con- 
tract. The exceptions can probably be explained 



532 THE OUTGO OF ENERGY 

as the effect of a constant 'stimulus (see page 
533). 

The apical half of the normal ventricle con- 
tains no nerve cells. Consequently its failure to 
contract after its separation from the remainder 
of the heart would indicate that the adult heart 
muscle is incapable of spontaneous rhythmical 
contraction. It has been shown, however, that the 
" apex " of the mammalian heart will beat after 
its complete removal from the remainder of the 
heart, provided the circulation in the extirpated 
piece is maintained by supplying it with blood. 

Rhythmic Contractility of Heart Muscle. — Fur- 
ther evidence of the rhythmic contractility of 
the heart muscle is found in the bulbus arteriosus. 

Place very small pieces of the bulbus arteri- 
osus in normal saline solution under the 
microscope. 

They will contract rhythmically. 

Histological examination shows that nerve 
cells seldom occur in the bulbus. It is scarcely 
credible that they are present in each of the small 
pieces seen contracting under the microscope. 

Constant Stimulus may cause Periodic Contrac- 
tion. — In a frog with ventricular apex isolated 
by Bernstein's ligature, compress one or both 
aortae, thus raising the pressure in the ventricle. 



THE CIRCULATION OF THE BLOOD 533 

The increased intracardiac pressure acts as a 
constant stimulus to the cardiac muscle and the 
hitherto inactive apex begins to contract again. 

Thus a constant stimulus may discharge peri- 
odic contractions in a muscle habituated to 
periodic contractions (compare page 144) ; the 
galvanic current and chemical stimuli, such as 
delphinin, are further examples of constant stim- 
uli which call forth rhythmic contractions of the 
heart muscle. 

The Inactive Heart Muscle still Irritable. — Stim- 
ulate the inactive " apex " mechanically and with 
single induction shocks. 

The apex, though incapable of spontaneous 
rhythmic contractions, is still irritable, and will 
respond by a single contraction to each stimulus. 

Refractory Period ; Extra-Contraction ; Compen- 
satory Pause. — Put the electromagnetic signal 
in the primary circuit. Connect the binding- 
posts on the heart-holder to the secondary coil of 
the inductorium. Arrange the latter for single 
induction currents. Place the ventricle on the 
heart-holder. Send maximal make and break 
induction currents through the ventricle from 
time to time in each phase of the cardiac cycle. 

Note that (1) the stimulus sometimes calls 
forth an extra-contraction ; (2) at other times 
the stimulus causes no contraction, having fallen 



534 THE OUTGO OF ENERGY 

into the ventricle during the period in which it 
is refractory towards stimuli ; (3) the extra-con- 
traction is followed by a pause, called the com- 
pensatory pause because it usually restores the 
rate of beat to that existing before the extra- 
contraction took place. 

Using induction currents of equal intensity, 
find the limits of the refractory period and note 
them on the drum. Note also the point in the 
cardiac cycle at which the maximum extra- 
contraction can be obtained. 

The Transmission of the Contraction Wave in the 
Ventricle ; Engelmann's Incisions. — The action 
current of the heart is taken to be an expression 
of the excitation process, although the nature of 
the latter is not yet understood. It has already 
been shown (page 310) that the action current 
sweeps rapidly over the ventricle preceding the 
contraction. The excitation might be propagated 
by nerves or by muscle fibres. The following 
experiment affords some evidence that the 
transmission is by means of muscular tissue. 

Leaving the heart in situ, cut the ventricle 
into a zigzag strip by obliquely transverse in- 
cisions beginning near the apex. The nerve 
fibres in the ventricle will thereby be severed 
at some part or other of their course, but muscular 
continuity will be preserved. 



THE CIRCULATION OF THE BLOOD 535 

The contraction wave will pass over the entire 
zigzag strip. Normally the wave starts at the 
base and proceeds to the apex, but by artificial 
stimulation it can be made to pass from the 
apex towards the base. A similar result can be 
secured with the auricle. 

The Transmission of the Cardiac Excitation from 
Auricle to Ventricle ; Gaskell's Block. — The con- 
traction wave can be seen to begin normally in 
the sinus and thence to pass rapidly over the 
auricle ; on reaching the auriculo-ventricular 
junction there is a distinct pause termed the 
auriculo-ventricular interval ; finally, the excita- 
tion reaches the ventricle, and the contraction 
wave is seen to traverse the ventricular muscle 
as noted above. The auriculo-ventricular inter- 
val may be lengthened by any natural or arti- 
ficial hindrance to the passage of the excitation 
wave. 

1. Place the Gaskell clamp about the auriculo- 
ventricular junction. Very cautiously turn the 
screw until the rubber edge makes a gentle 
pressure on the cardiac tissues at that point. 

With careful work a degree of pressure will be 
reached that diminishes the conductivity of the 
muscle fibres joining the auricle and ventricle so 
far as to permit only every second or every third 
excitation to pass. The auricle will beat with- 



536 THE OUTGO OF ENERGY 

out change of frequency, but the ventricle will 
contract only when the excitation succeeds in 
passing the block. 

2. Divide the auricles in two pieces con- 
nected by a small bridge of auricular tissue. 
Stimulate one piece. 

The stimulation of one piece will be followed 
immediately by the contraction of that piece, 
and, after an interval, by the contraction of the 
other. The smaller the bridge, the longer the 
interval. 

Gaskell has pointed out that a natural block 
is furnished by the small number of the muscle 
fibres joining the auricle to the ventricle, and 
that this natural block explains the auriculo- 
ventricular interval, i. e. the delay which the 
excitation experiences in passing from the auricle 
to the ventricle. 

3. Eepeat Experiment 1, but place the screw- 
clamp across the middle of the ventricle. 

The passage of the excitation from one part of 
the ventricle to another will be delayed or inter- 
rupted by the lowering of the conductivity in 
the compressed portion. 

Many irregularities in the frequency and force 
of the heart can be explained by variation in the 
conductivity of its several parts. They can be 



THE CIRCULATION OF THE BLOOD 537 

explained also by variations in the irritability of 
the several parts. In the latter case, the excita- 
tion would pass as usual, but its action on any 
part, for example the ventricle, would be in- 
creased or diminished by changes in the irri- 
tability of the cardiac muscle in that region. 
Engelmann has found that ventricular systole 
lowers the conductivity of the ventricle for a 
time. 

Tonus. — Pass the very fine copper wire through 
the wall of the auricle of the tortoise and attach 
the wire to the heart lever, so that the contrac- 
tions of the auricle may be recorded. Let the 
drum move so slowly that the individual contrac- 
tions will be nearly but not quite fused. 

Two sorts of contractions can be distinguished, 
(1) the usual frequent contraction or beat of the 
auricle, (2) the tonus oscillations. The tonus 
oscillations include from twenty to forty beats. 
In the tortoise auricle, the beats usually become 
less extensive during the rise of tonus. 

The Influence of "Load" on Ventricular Contrac- 
tion. — Eecord the contractions of the frog's 
ventricle. Increase the intraventricular pressure 
(i. e. the load against which the ventricular muscle 
contracts) by clamping the aortse with forceps 



538 THE OUTGO OF ENERGY 

the blades of which are covered with rubber 
tubing. 

The force of the individual contractions 
will be increased but their frequency will be 
diminished. 

The Influence of Temperature on Frequency of 
Contraction. — Let the drum move at such a 
speed that the individual heart-beats in the 
curve shall be close together, but yet separate 
and distinct. Surround with normal saline solu- 
tion at 25° C. 

The frequency of contraction will be increased. 

Eeplace the warm solution with normal saline 
solution at 5° C. 

The frequency of contraction will be dimin- 
ished. 

The Action of Inorganic Salts on Heart Muscle. — 
Sever the apical two-thirds of the ventricle of the 
tortoise heart from the remainder of the ventricle 
by a cut parallel with the auriculo-ventricular 
furrow. With a second parallel cut remove 
from the severed portion a ring two or three 
millimetres wide. Divide the ring to form a 
strip. Fasten one end of the strip to the short 
limb of a glass rod bent at a right angle. By 
means of a silk thread connect the other end of 
the strip to a heart lever arranged to record the 



THE CIRCULATION OF THE BLOOD 539 

contractions of the strip on a very slowly moving 
drum. 

Sodium. — Immerse the strip of ventricular 
muscle in a beaker containing 0.7 per cent solu- 
tion of sodium chloride. 

After a latent period, which may be protracted, 
but usually is brief, a series of rhythmic con- 
tractions will be observed. The contractions 
soon reach a maximum and then gradually die 
away. Sodium, although an important stimulus 
to contraction, cannot maintain the ventricle in 
continued activity. 

The tonus of the heart muscle is diminished 
by sodium chloride. 

Calcium. — Surround a strip of contracting 
ventricular muscle with a solution of calcium 
chloride isotonic with 0.7 per cent sodium chlo- 
ride solution (approximately 1.0 per cent). 

Contractions will cease. Calcium added to 
solutions of sodium chloride, however, will 
lengthen the period during which the heart 
muscle contracts and will increase the strength 
of the individual contractions. Strong solutions 
of calcium chloride greatly increase the tonus. 

Potassium. — Surround a non-beating strip of 
ventricular muscle witli a solution of potassium 
chloride isotonic with 0.7 per cent sodium 
chloride solution (approximately 0.9 per cent). 



540 THE OUTGO OF ENERGY 

Contractions will not be produced. If potas- 
sium be applied to a contracting strip, the con- 
tractions will cease. 

Combined Action of Sodium, Calcium, and 
Potassium. — Surround the ventricular muscle 
with a solution containing sodium chloride (0.7 
per cent), calcium chloride (0.0026 per cent), 
and potassium chloride (0.035 per cent). This 
is a modified " Einger " solution. 

Long-continued, rhythmic contractions will be 
secured. 

Observers are not entirely agreed as to the 
action of potassium and calcium on heart muscle. 
The matter is of importance because there is 
much probability that the rhythmic contractions 
of the heart are the result of the constant chemi- 
cal stimulus of inorganic salts present in the 
blood. Most observers are agreed that the inter- 
action of salts of sodium, calcium, and potassium 
is essential. 

The fact that the contraction of the heart 
begins normally in the sinus may be due to a 
greater sensitiveness of that part to chemical 
stimulation. 



THE CIRCULATION OF THE BLOOD 541 



The Heart Sounds 

With a binaural stethoscope auscultate the 
chest over its entire extent during normal respi- 
ration and while the subject holds his breath. 

1. Note that two sounds are heard in the 
heart region. 

2. Determine at what point each of the sounds 
is most distinct. 

It will be found that one, termed the "first 
sound," will be most distinct where the ventricle 
comes nearest the surface, near the apex of the 
heart, in the space between the fifth and sixth 
ribs, about 2.5 cm. below and 2.5 cm. within the 
left nipple. Close inspection of this region in 
persons not too fat will show that the chest wall 
is raised at each contraction of the heart. The 
cardiac impulse, as it is called, may be felt dis- 
tinctly by one or two fingers laid in the fifth 
intercostal space. It is caused by the rapid 
increase in the tension of the ventricle. 

The " second sound " will be heard most dis- 
tinctly immediately over the aortic arch, near the 
junction of the second right costal cartilage with 
the sternum. 

3. Observe the two sounds with relation to 
their duration, pitch, intensity, and quality. 



542 THE OUTGO OF ENERGY 

The first sound iu comparison with the second 
is of longer duration, lower pitch, and greater 
intensity. The quality of the first sound is dull, 
booming ; that of the second is sharp, valvular. 

4. With one finger feeling the cardiac impulse 
observe the sounds with reference to systole and 
diastole. 

The first sound will be found to be systolic, 
i. e. it occurs with the contraction of the ventricle, 
while the second sound is diastolic, being heard 
at the beginning of ventricular relaxation. The 
interval between the first and second sounds is 
therefore very brief. The pause after the second 
sound before the first is heard again, is consider- 
ably longer. 

The first sound can be heard in the extirpated, 
bloodless heart (dog). The contraction of the 
ventricular muscle is therefore alone sufficient 
for its production. But the sound is modified or 
replaced by a murmur when the auriculo-ven- 
tricular valves are sufficiently injured. It is 
probable, therefore, that the sudden increase in 
the tension of the auriculo- ventricular valves con- 
tributes to its production. The second sound 
obviously is due to the sudden increase in the 
tension of the semilunar valves. It is replaced 
by a murmur when these valves are rendered 
incompetent. 



THE CIRCULATION OF THE BLOOD 543 

Ordinarily the ratio between the blood-pressure 
in the pulmonary artery and right ventricle so 
nearly equals the ratio between the blood 
pressure in the aorta and left ventricle that the 
semilunar valves in the pulmonary artery and 
aorta close together, or nearly together, and their 
respective sounds are heard as one. Pathologic- 
ally, for example in distention of the right heart 
from prolonged violent exercise, these relations 
may be so altered as to produce between the two 
sounds an interval perceptible to the ear. The 
sound is then said to be reduplicated. 

The Pressure-Pulse 

Frequency. — Palpate the radial pulse by 
laying on the artery at the wrist the ball (not 
the tip) of the first, second, and third fingers of 
the right hand. The forearm of both subject 
and observer should be supported in a comfort- 
able position. Count the pulse in four successive 
periods of fifteen seconds. The counting of the 
observer's instead of the subject's pulse may be 
avoided by noting whether the subject's supposed 
pulse is synchronous with the observer's heart- 
beat. 

Note the frequency per minute when the sub- 
ject is standing, sitting, lying, swallowing, hold- 
ing the breath ; and before and after exercise ; 



544 THE OUTGO OF ENERGY 

for example, before and after lifting the weight 
of the body ten times by rising on the toes. 

Sex, eating, the time of day, the temperature, 
and many other factors also influence the fre- 
quency of the pulse. 

Hardness. — When pressure is made upon an 
artery in any part of its course, the pressure is 
transmitted in all directions through the liquid 
contained in the peri-arterial tissues, and the 
artery becomes smaller. Part of the pressure is 
used upon the peri-arterial tissues themselves. 
When the remaining pressure equals the maxi- 
mum blood-pressure in the artery at the point of 
compression, the blood-pressure on the distal 
side of this point will sink to the level of the 
blood-pressure in the nearest anastomosis. If 
the anastomosis is of capillary size, the pulse will 
disappear. A pulse which is obliterated by slight 
pressure is termed " soft ; " if the pressure re- 
quired is relatively considerable, the pulse is 
termed " hard." The hardness of the pulse is 
therefore a measure of the maximum blood- 
pressure at the point of compression, less the 
variable and unknown quantity required for the 
compression of the elastic tissues. 

Form. — 1. The vibrations which follow the 
primary pulse wave cannot ordinarily be recog- 
nized by the palpating finger. When, however, 



THE CIRCULATION OF THE BLOOD 545 

the usual amplitude of the principal secondary 
vibration is much increased and the interval be- 
tween the primary and this secondary vibration 
is not too brief, the pulse may be felt to be 
double, or " dicrotic." For example, dicrotism 
can be felt in some cases of continued fever. 

2. A pulse which is felt to reach its maximum 
slowly is called a " slow pulse " (pulsus tardus). 
One which reaches its maximum rapidly, giving 
the palpating finger the sensation of a quick 
push, is said to be a " quick pulse " (pulsus celer). 
Quick and slow pulses should be carefully dis- 
tinguished from frequent and infrequent pulses. 

Volume. — The extent to which the arterial 
wall is driven from its position of equilibrium 
(volume or size of pulse) is a function of the 
output of the ventricle, the outflow period, 
the peripheral resistance, and the elasticity of 
the arteries. It is measured very inexactly by 
the palpating finger and the sphygmograph, accu- 
rately by the plethysmograph (page 552). 

The Pressure-Pulse in the Artificial Scheme. - — • 
Eevolve the disk of the artificial scheme until 
the arterial pressure is maintained at 50 mm. 
Hg. Close the tube leading to the arterial 
manometer, so that the oscillations of the 
mercury may not influence the curves to be 
taken. Attach the small thistle-tube (without 

35 



546 THE OUTGO OF ENERGY 

rubber membrane) to the sphygniograph (Fig. 
70) and adjust the tube upon the aorta. Close 
the side branch of the sphygmograph tube. Bring 
the writing point of the sphygmograph lever 
against a slow-moving, lightly-smoked drum. 
Kecord a series of pulse curves. 

Note the quick upstroke, corresponding bo the 
quick distention of the artery by the emptying 
of the ventricle, and the gradual downstroke, 
corresponding to the gradual emptying of the 
artery through the resistance during the diastole 
or interval between two beats. Near the apex 
of the more delicately written curves may be 
seen a slight depression, the dicrotic notch. 

It is obvious that the changes observed in the 
size of the artery are the expression of changes 
in the blood-pressure. The pulse is a function 
of the blood-pressure at the point observed. 
Hence the term pressure-pulse. 

The Human Pressure-Pulse Curve. — 1. Adjust 
the lever of the recording tambour so that it shall 
write with the least friction possible on a thinly 
smoked drum. Let the drum revolve slowly 
(two revolutions a minute). Be sure that the 
side branch is open. Place the larger thistle- 
tube, which serves as a "receiving tambour," 
over the carotid artery, anterior to the stern o- 
cleidomastoideus muscle, about the level of the 



THE CIRCULATION OF THE BLOOD 547 

thyroid cartilage. When the tambour (without 
rubber membrane) is pressed well down over the 
artery, let an assistant close the side branch. If 
the receiving tambour has been properly placed, 
the recording tambour will write a sharply 
marked pulse curve. If none such appears, open 
the side branch and move the receiving tambour 
into a better position. 

Indicate the primary wave, the predicrotic 
elevation, and the dicrotic notch. 

2. Cover the thistle-tube with a rubber mem- 
brane. Cement in the centre of the membrane a 
bone collar-button. Place the button upon the 
radial artery at the wrist and record the radial 
pulse. 

It will be found that the degree of pressure 
must be carefully regulated in order to secure a 
satisfactory curve. The blood-pressure in the 
artery normally is held in equilibrium by the 
elastic tension of the wall of the artery and the 
surrounding tissues. The pressure of the sphyg- 
mograph increases the tension of the peri-arterial 
tissues and thus assists in holding the blood- 
pressure in equilibrium. The greater the pres- 
sure of the sphygmograph, the larger the part of 
the blood-pressure borne by it and the more com- 
pletely will variations in the blood-pressure be 
made visible in the pulse curve. The record, 



548 THE OUTGO OF ENERGY 

however, is not a measure of the absolute blood- 
pressure, because it is not possible to estimate 
accurately how much of the blood-pressure is 
still held in equilibrium by the elastic tension 
of the arterial wall and the surrounding tissues. 
The pulse curve does give with approximate 
correctness the variations in the blood-pressure. 
The correctness would be complete were it not 
that the part of the blood-pressure held in 
equilibrium by the elastic tension of the arterial 
wall varies with the size of the vessel, and the 
size of the vessel increases as the blood-pressure 
increases. Thus the portion of the blood-pres- 
sure which fails of record constantly varies. 
The error thus introduced is not important. 
The sphygmograph, therefore, gives a practically 
true record of the form of the pulse, i. e. the 
time-relations of the changes in blood-pressure. 
This knowledge cannot possibly be secured by 
the palpation of the pulse. The sphygmograph, 
it may be repeated, does not give a true record 
of the absolute blood-pressure (hardness) or of 
the amplitude (size) of the pulse. Both hardness 
and amplitude are better measured by the pal- 
pating finger. 

In many sphygmographs, for example, Marey's 
and Dudgeon's, the pressure on the artery is 
made by a metal spring, the movements of which 



THE CIRCULATION OF THE BLOOD 549 

are recorded by a lever. In the record just taken 
from the radial artery, the pressure was made by 
the elastic tension of the rubber membrane clos- 
ing the thistle-tube. In the case of the carotid 
artery, this membrane is replaced by the skin of 
the neck. 

In every instance, the sphygmograph records 
the changes of blood-pressure in a section of the 
artery so short in comparison with the length of 
the whole arterial tree as to be practically a 
cross-section. 

Low Tension Pressure-Pulse. — 1. In the arti- 
ficial scheme open slightly the side-branch that 
permits the liquid in the arterial tubes to flow 
out without passing through the resistance. The 
arterial pressure will fall in consequence of the 
diminished peripheral resistance. Normally this 
effect is produced by a dilatation of the smaller 
arteries. Let the arterial pressure fall to about 
20 mm. Hg. Kecord a series of pulse curves. 

Note that the oscillations of the mercury 
column with each ventricular beat are much 
higher than with normal pressure (120-150 mm.). 
Feel the pulse with the finger. With each boat 
the artery quickly expands and as quickly re- 
laxes. The artery is "softer" than usual. 

2. Feel the normal pulse in the radial artery. 
Note the normal " hardness." Let the subject 



550 THE OUTGO OF ENERGY 

inhale two drops (on no account more than two) 
of the nitrite of amyl (to be dropped on a hand- 
kerchief by one of the instructors). This power- 
ful drug causes dilatation of the blood vessels, 
particularly the smaller arteries. 

Observe that as the face flushes, indicating the 
vascular dilatation, the pulse will be softer. 

Do not repeat the experiment. 

Pressure-Pulse in Aortic Regurgitation. — Empty 
the principal tubes of the artificial scheme. Ee- 
move the rubber from about the aortic valve. 
Eeplace the valve tube. Fill the apparatus with 
water. Eevolve the disk at the rate and with 
the force employed to imitate the normal circula- 
tion (page 545). 

Feel the pulse with the finger. 

After each systole the liquid streams back 
through the incompetent valve. The ventricle 
is thus fuller than normal at the beginning of 
the stroke, while the arteries are less than 
normally full. Consequently more than the 
usual quantity is discharged by the ventricle 
into relatively undistended arteries. The rela- 
tively lax artery is thereby quickly and largely 
expanded, as indicated by the quick thrust given 
the palpating finger and by the large excursion 
of the mercury in the arterial manometer. 

Eecord pulse curves. 



THE CIECULATION OF THE BLOOD 551 

The upstroke is unusually high and quick. It 
is at once followed by a great and sudden fall. 
Obviously a relatively empty artery has been 
suddenly filled by an unusually large inflow and 
has been suddenly emptied again through the 
broken valve and the capillaries. The pulse- 
curve shows low arterial tension, but is of greater 
amplitude than the pulse in which low tension 
results from lowering the peripheral resistance. 
In the body, the amplitude of the pulse in aortic 
regurgitation is increased by the greater force 
with which the ventricle contracts, as well as by 
the larger quantity discharged at each beat, for 
the back-flow from the aorta dilates the ventricle 
and usually causes the walls of the ventricle to 
increase in thickness (dilatation with hypertrophy 
of the ventricle). 

Stenosis of the Aortic Valve. — Replace the rub- 
ber flap upon the aortic valve-tube, and tie a 
string around the flap and tube just over the 
opening in the tube. Stenosis, i. e. narrowing, of 
the opening will thus be secured. Put the valve- 
tube in place, and compress the bulb at the usual 
rate. Record pulse curves. 

The slow difficult emptying of the ventricle 
will be evident in the curve and to the hand. 
The movements of the arterial manometer are 
sluggish and of diminished amplitude. The 



552 THE OUTGO OF ENERGY 

pulse wave is small and the upstroke slow, 
corresponding to the small slow inflow through 
the stenosed valve. 

Restore the valve to its normal state. 

Incompetence of the Mitral Valve. — Remove 
the rubber flap from the mitral valve. Eecord 
pulse curves as before. 

The pulse will be small, because the pressure 
in the auricle (in this case the reservoir of water) 
is always low, while the pressure in the arteries 
is always high. Hence the ventricle will partly 
empty itself through the incompetent mitral 
valve, in the direction of low resistance, before 
the pressure in the ventricle rises high enough to 
open the aortic valve against the high aortic 
pressure. The quantity remaining in the ventri- 
cle when the intraventricular pressure rises high 
enough to open the aortic valve is not sufficient 
to distend the arteries to the normal degree. 

In mitral stenosis the pulse is also small 
because the narrowing of the mitral orifice per- 
mits less than the usual quantity of liquid to 
enter the ventricle. 

The Volume Pulse 

Remove the receiving tambour of the sphygmo- 
graph from its tube, and insert the pie thy sino- 
graph cylinder (this is the tube used in the 



THE CIRCULATION OF THE BLOOD 553 

experiment on the volume of contracting muscle, 
Tig. 58). Place the middle finger in the cylinder, 
making sure that the rubber collar fits around 
the finger tightly, but without impeding the 
venous circulation. Close the side branch. 

Periodical alterations in the volume of the 
finger will be recorded ; they have the rhythm of 
the heart-beat. (The friction of the writing-lever 
must be very slight to insure success, and the 
curve at best will be small.) 

Determine the effect of straining and forced 
respiration upon the curve. 

Apparatus 

Normal saline. Bowl. Towel. Pipette. Artificial 
scheme. Microscope. Mesentery board. Mercury man- 
ometer. Aortic cannula. One per cent solution of sodic 
carbonate. Ligature. Glass rod one inch long. Frog- 
board. Wooden stand. Kymograph. Inductorium. Dry 
cell. Electrodes. Key. Electromagnetic signal. Sphyg- 
mograph with large anu small thistle-tubes. Rubber 
membrane. Bone collar-button. Heart-holder. Screw- 
clamp. Muscle lever with scale-pan and weights. Stand. 
Fine copper wire. Tortoise with heart exposed. Ice. 
Solution of sodium chloride, 0.7 per cent. Solutions of 
calcium chloride, and potassium chloride, each isotonic 
with 0.7 per cent solution of sodium chloride. A solu- 
tion containing sodium chloride, 0.7 per cent ; calcium 
chloride, 0.026 per cent; and potassium chloride, 0.035 
per cent. Binaural stethoscope. Nitrite of amyl. Ple- 
thysmograph. 



554 THE OUTGO OF ENERGY 



XIII 

THE INNERVATION OF THE HEART AND 
BLOOD-VESSELS 

The quantity of blood required by the tissues 
varies from time to time. For example, the 
digestive organs require more blood when food 
is taken than at other times. Variations in the 
blood supply of the individual organs are accom- 
plished chiefly by varying the size of their blood 
vessels. To this end the blood vessels are pro- 
vided with muscular coats which are made to 
contract or relax, and thus to constrict or dilate 
the vessels. The impulse to contraction or relax- 
ation is given by the vasomotor nerves. It is 
necessary, too, that the force and frequency of 
ventricular contraction should vary with the 
resistance to be overcome, the need for more 
rapid oxygenation of the blood, etc., and special 
nerves are provided for this purpose also. The 
control or innervation of the heart and blood 
vessels will now be considered. 

The heart is provided with nerves that aug- 
ment and nerves that inhibit its action. 



innervation of heart and blood-vessels 555 

The Augmentor Nerves of the Heart 

In the frog both the augmentor and the inhibi- 
tory nerves reach the heart through the splanch- 
nic branch of the vagus. The augmentor fibres 
leave the spinal cord in the third spinal nerve, and 
pass through the ramus communicans of this 
nerve into the third sympathetic ganglion, where 
they probably end in contact with the body or 
processes of sympathetic cells. The axis-cylin- 
ders of these sympathetic cells pass up the cer- 
vical sympathetic chain to the ganglion of the 
vagus (Fig. 72), and thence down the vagus trunk 
to the heart. Thus in the greater part of its 
course the vagus cannot be stimulated without 
exciting both the augmentor and the inhibitory 
cardiac fibres. To excite either alone it is neces- 
sary to stimulate the respective nerves above 
their junction. 

Preparation of the Sympathetic. — Cut away the 
lower jaw of a large frog, the brain of which has 
been destroyed by pithing, and continue the slit 
from the angle of the mouth downwards for a 
short distance. Avoid cutting the vagus nerve 
(Fig. 73). Turn the parts well aside, and ex pose 
the vertebral column where it joins the skull. 
Kemove the mucous membrane, covering the 
roof of the mouth. The sympathetic is situated 



556 



THE OUTGO OF ENERGY 



immediately under the levator anguli scapulae 
muscle, which must be carefully removed. The 
nerve will then be visible. It is commonly pig- 
mented and usually lies under an artery. Care- 
fully isolate the nerve. Put a ligature around it 



K 




LAS 



Fig. 72. Scheme of the sympathetic nerve in the frog. OC. Occiput. 
LAS. Levator anguli scapulae. Sym. Sympathetic. GP. Glosso-pharyn- 
geus. V-S. Vago-sympathetic. G. Ganglion of the vagus. Ao. Aorta. 
SA. Subclavian artery. (After Stirling's reproduction of Gaskell and 
Gadow's plate.) 



as far away from the skull as practicable, and 
cut the nerve caudal to the ligature. 

Action of the Sympathetic on the Heart. — 
Arrange the inductorium for weak tetanizinsr cur- 
rents. In the primary circuit place the electro- 



INNERVATION OF HEART AND BLOOD-VESSELS 557 

magnetic signal. Prepare the sympathetic as 
directed above. Expose the heart (page 75). 
Place it in the heart-holder. Should the heart 
beat rapidly, slow it with ice. Let the writing 
point record above the point of the electromag- 
netic signal on a drum revolving so slowly that 
the individual beats shall appear in the curve 
very close together, yet far enough apart to be 
readily counted. Divide the observation into 
nine periods of twenty seconds each. Place the 
electrodes beneath the sympathetic, with the 
short-circuiting key closed. Adjust the heart 
lever to write its curve. Let the assistant call 
the beginning of each period as he marks it on 
the drum. At the beginning of the second pe- 
riod, open the short-circuiting key ; at the begin- 
ning of the third period, close the short-circuiting 
key. Lower the drum when one circuit is 
completed. 

Count the number of beats in each period. The 
frequency will be increased. The force of con- 
traction will also be increased. 1 The latent period 
of excitation is long and there is a prolonged 
after-effect. The former frequency is regained 
more rapidly after short than after long stimula- 
tions. The speed of the cardiac excitation wave 

1 The stimulation of the augmentor fibres is difficult and 

often fails in winter frogs. 



558 



THE OUTGO OF ENERGY 



(compare page 336) is increased and the time of 
its passage across the auriculo-ventricular groove 
is shortened, though this cannot be observed by 
the method used in the present experiment. 

The Inhibitory Nerves, of the Heart 

The Preparation of the Vagus Nerve. — Fasten 
a lame frog on the board, back down. Pass the 




Fig. 73. Scheme of the cervical nerves in the frog (after Schenck). 
G. P. Glosso-pharyngeus. Hg. Hypoglossus. V. Vagus. L. Laryngeus. 
K. Posterior end of lower jaw. The glosso-pharyngeus has been drawn 
to one side of the hypoglossus for the sake of clearness. 

glass tube through the oesophagus into the 
stomach. Eemove the muscles lying over the 
petrohyoid muscle, which passes from the base of 
the skull to the horn of the hyoid bone. Lying 



INNERVATION OF HEART AND BLOOD-VESSELS 559 

near the line between the angle of the jaw and 
the auricle are four nerves (Fig. 73) : (1) The 
hypoglossus. This nerve is superficial. Near 
their emergence from the skull it is the lowest 
of the nerves, but later, the uppermost. It crosses 
the remaining nerves and the blood-vessels, and 
passes forwards and inwards towards the tongue. 
(2) The glosso-pharyngeus, which soon turns for- 
wards beneath the hypoglossus parallel to the 
ramus of the jaw. (3) The vagus, and (4) the 
laryngeus, the two lying almost parallel in the line 
between the angle of the jaw and the auricle. 
The laryngeus rests on the petrohyoid muscle, and 
passes upwards and inwards beneath the arteries 
towards the larynx. The vagus runs at first 
along the superior vena cava to the auricle ; a 
branch is given off to the lungs. Clear the vagus, 
tie a silk thread around the nerve and sever the 
nerve on the cranial side of the ligature, so that 
the peripheral stump can be placed on the elec- 
trodes for stimulation. Divide the laryngeal 
branch. Keep the preparation moist with nor- 
mal saline solution. 

Stimulation of Cardiac Inhibitory Fibres in 
Vagus Trunk. — Arrange the inductorium for 
weak tetanizing currents. In the primary circuit 
place the electro-magnetic signal. Expose the 
heart. Place it in the heart-holder. Let the 



560 THE OUTGO OF ENERGY 

writing point record exactly above the point of 
the electromagnetic signal on a drum revolving so 
slowly that the individual beats shall appear in 
the curve very close together and yet far enough 
apart to be readily counted. 

Lay the vagus nerve on the electrodes. Start 
the drum. As soon as good curves are writing, 
start the inductorium, and open the short-circuit- 
ing key for about twenty seconds. The heart will 
be inhibited. Note that the arrested heart is al- 
ways relaxed, i. e. in diastole. The latent period 
is short (one or two heart-beats). A brief after- 
effect is present. If the stimulus is continued, 
the heart will begin to beat even during the 
stimulation, showing that the inhibitory mechan- 
ism can be exhausted. The heart beats more 
rapidly, and usually more strongly, immediately 
after inhibition than before ; this probably is due 
to the after-effect of the stimulation of augmentor 
fibres in the vagus trunk, as explained below. 

Eepeat the stimulation, but weaken the stimu- 
lating current by moving the secondary farther 
from the primary coil. 

With a suitable strength of current, the heart 
will be slowed but not arrested. The duration 
of diastole will be markedly less, while the dura- 
tion of systole will be changed but little if at 
all. A stronger excitation would lengthen both 



INNERVATION OF HEART AND BLOOD-VESSELS 56 L 

systole and diastole. The diminution in force often 
appears before the diminution in frequency. 

Effect of Vagus Stimulation on the Auriculo-Ven- 
tricular Contraction Interval. — Counterpoise two 
inverted muscle levers. Place their writing points 
exactly above the writing point of the electro- 
magnetic signal. Pass fine bent pins through 
the auricle and ventricle, respectively, and con- 
nect them by silk threads with the muscle levers 
("Suspension method"). Let the drum revolve 
at its fastest speed. When good auricular and 
ventricular contractions are obtained, stimulate the 
vagus trunk with a current not quite sufficient to 
cause arrest. 

Note that the inhibition affects both the auricle 
and the ventricle. Weak stimuli affect primarily 
the auricles. The auriculo-ventricular contrac- 
tion interval is lengthened. 

Irritability of the Inhibited Heart. — Arrest the 
heart by stimulating the vagus trunk. When 
complete inhibition is secured, touch the ventricle 
smartly with the point of the seeker. 

The ventricle will respond by a single contrac- 
tion. 

When the inhibition is profound, the irritabil- 
ity may be so far reduced that the heart will not 
contract on direct stimulation. 

In addition to the effects already enumerated, 

36 



562 THE OUTGO OF ENERGY 

appropriate methods of observation would show 
that vagus excitation increases the intraventricu- 
lar pressure during diastole, lessens the intake 
and the output of the ventricle, and diminishes 
the tonus of the heart muscle. The action of the 
vagus is accompanied by a positive electrical 
variation. The action on the sinus and on the 
bulbus does not differ essentially from that upon 
the ventricle. 

It has already been pointed out that the vagus 
of the frog contains both inhibitory and augment- 
ing fibres. The stimulation of the mixed nerve 
usually causes inhibition, as described above, but 
sometimes augmentation. The augmentation ob- 
served after cessation of the inhibitory effect is 
probably explained by the longer after-effect of 
the augment or excitation. 

Intracardiac Inhibitory Mechanism. — Arrange 
an inductorium for tetanizing currents. Close 
the short-circuiting key. Expose a frog's heart. 
Eaise the heart with a glass rod. Note the white 
" crescent " between the sinus venosus and the 
right auricle. Set the inductorium in action. 
Put the points of the electrodes on the crescent, 
and open the short-circuiting key for a moment. 
After one or two beats the heart will stop. 

Inhibition by Stannius Ligature. — Turn up the 
heart to expose its posterior surface, and note the 



INNERVATION OF HEART AND BLOOD-VESSELS 563 

line of junction of the sinus venosus and right 
auricle. Tie a ligature around the heart exactly 
at this line, passing the thread beneath the aortas, 
so that they shall not be included in the ligature. 

The auricles and ventricle cease to beat, for a 
time at least, while the sinus venosus continues 
with unaltered rhythm. (The result is usually 
ascribed to inhibition, from the mechanical stim- 
ulation of the intracardiac inhibitory mechanism. 
If the ventricle begins spontaneously to beat, as 
may happen if the ligature is not accurately 
placed, tie a second ligature around the junction 
of sinus and auricle.) 

Action of Nicotine. — Apply nicotine solution 
(0.2 per cent) to the ventricle. After a few 
minutes, stimulate the trunk of the vagus nerve. 
No curve need be written. 

The heart is not inhibited. 

Now lift the heart with a glass rod, and stimu- 
late the intracardiac inhibitory nerves. 

The heart is inhibited. Nicotine paralyzes 
some inhibitory mechanism between the vagus 
and the intracardiac inhibitory nerves. But it is 
known that nicotine does not paralyze nerve 
trunks. Hence it is probable that the cardiac 
inhibitory fibres do not pass to the cardiac muscle 
directly, but end in contact with nerve cells, 
which take up the impulse and transmit it 



564 THE OUTGO OF ENERGY 

through their processes to the muscular fibres of 
the heart. 

Atropine. — With a clean pipette apply a few 
drops of a solution of atropine (0.5 per cent) to 
the heart. After a few moments lift the ventri- 
cle and stimulate the crescent. 

The heart is not inhibited. Atropine paralyzes 
the intracardiac inhibitory nerves. 

Muscarine. — With a line pipette put upon the 
ventricle a few drops of normal salt solution con- 
taining a trace of muscarine (a poisonous alkaloid 
extracted from certain mushrooms). 

The ventricle will gradually be arrested in 
diastole, much distended with blood. 

Antagonistic Action of Muscarine and Atropine. 
— With a fresh pipette apply a little normal salt 
solution of atropine (0.5 per cent). 

The heart will commence to beat again. 

o 

The Centres of the Heart Nerves 

It has been shown that the heart receives in- 
hibitory and augmenting nerve fibres. The sit- 
uation of the inhibitory and augmenting " centres," 
i. e., the nerve cells from which the inhibitory 
and augmenting fibres spring, should now be 
considered. 

Inhibitory Centre. — Place a frog and a small 
sponge wet with ether under a glass jar. Be very 



INNERVATION OF HEART AND BLOOD-VESSELS 565 



careful not to kill the frog by an overdose of 
ether. When insensibility is complete, place the 
animal, back uppermost, on 
a frog-board. Cut through 
the skin in the median line 
from the nose about half 
way to the urostyle. Care- 
fully uncover the roof of the 
skull. Eemove the longitu- 
dinal muscles on either side 
of the 1st, 2d, and 3d verte- 
brae. Strip off the parietal 
bones with forceps, begin- 
ning at the anterior end, 
opposite the anterior margin 
of the orbit. Clear away 
the occipital bones. Saw 
through the laminae of the 
first three vertebras, and re- 
move the laminae to expose 
the spinal cord. Expose the 
heart by cutting away the 
chest wall over the pericar- 
dium. Hold the frog in such 
a way that the heart can be 
observed while the brain and 
cord are stimulated. With 
needle electrodes, the points 




Fig. 74. View of the brain 
of a frog from above, en- 
larged. L.ol. Olfactory lobes. 
H.c. Cerebral hemispheres. 
G.p. Pineal body. Th.o. 
Optic thalami. L.op. Optic 
lobes. C Cerebellum. M.o. 
Medulla oblongata. S.rh. 
Sinus rhomboidalis. (After 
Foster's plate in Burdon- 
Sanderson's Handbook.) 

of which should be 



566 THE OUTGO OF ENERGY 

one millimetre apart, stimulate the spinal cord 
with a tetanizing current of a strength easily 
borne on the tongue. 

Stimulation of the spinal cord will not inhibit 
the heart. Stimulation of the cerebral hemi- 
spheres will be also ineffectual. Now stimulate 
the medulla oblongata. (Fig. 74.) 

The heart will be inhibited. 

This method of locating the cardio -inhibitory 
centre is unsatisfactory, because the inhibition 
produced may possibly be the result of the stimu- 
lation of nerve paths to or from the centre. Its 
results can be controlled by the method of suc- 
cessive sections, to be explained in connection 
with the vasomotor centre, page 565. 

The cardio-inhibitory centre is always in ac- 
tion, for section of the vagi causes the heart to 
beat more frequently. 

Augmentor Centre. — It is probable that this 
centre, like the inhibitory centre, is situated in 
the bulb, but the location is not definitely known. 
The constant activity of the augmentor centre is 
shown by the fall in frequency of beat after sec- 
tion of the vagi followed by bilateral extirpation 
of the inferior cervical and first thoracic ganglia 
in mammals. 

The neuraxons, or axis-cylinder processes, of 
the augmentor cells lying in the central nervous 



INNERVATION OF HEART AND BLOOD-VESSELS 567 

system pass out of the spinal cord in the white 
rami and terminate in the sympathetic ganglia 
(for example, the inferior cervical and stellate 
ganglia of the dog) in contact with sympathetic 
cells, the neuraxons of which convey the impulse 
to the heart. 

The cardiac centres are readily affected by 
afferent impulses from many sources. 

Reflex Inhibition of the Heart; Goltz's Experi- 
ment. — In a very lightly etherized frog, expose 
the pericardium by cutting away the chest wall 
over the heart. Count the number of beats in 
periods of twenty seconds. Continue the count 
while an assistant strikes gentle blows with the 
handle of a scalpel upon the abdomen at the rate 
of about 140 per minute. 

The frequency will usually diminish and, in fa- 
vorable cases, the heart will at length be arrested. 

Cut both vagus nerves and repeat the experi- 
ment. 

The reflex inhibition of the heart cannot be 
obtained after section of the vagi. 

It has been shown by Bernstein that the affer- 
ent nerves in this experiment are abdominal 
branches of the sympathetic nerve. The stim- 
ulation of the central end of the abdominal 
sympathetic in the rabbit also produces reflex 
inhibition of the heart. 



568 THE OUTGO OF ENERGY 

Reflex Augmentation. — Count the human radi- 
al pulse during four consecutive periods of fifteen 
seconds. Let the subject sip cold water slowly. 
Eepeat the count while the subject swallows. 

The frequency will be increased. 

Variations in the force and frequency of the 
heart-beat follow the stimulation of most afferent 
nerves, for example the central end of the divided 
vagus, the sciatic, and other mixed nerves, the 
nerves of special sense, and the afferent nerves 
which arise in the heart and pass to the bulb. 

The most conspicuous of the nerves which bear 
impulses from the heart to the central nervous 
system in mammals is the depressor. This nerve 
occurs as an isolated trunk in the rabbit, and is 
found mixed with other fibres, for example in the 
vagus, in many other animals. The stimulation 
of the end of the severed depressor nerve in con- 
nection with the heart is without effect. The 
stimulation of the end in connection with the 
bulb slows the heart and dilates the blood-vessels, 
thus causing a great fall in the blood-pressure. 

The Innervation of the Blood-Vessels 

The Bulbar Centre. — 1. Lightly etherize a large 
frog. Expose and cut both vagus nerves (in 
order to exclude inhibition of the heart). It is 
of the first importance to avoid excessive hemor- 



INNERVATION OF HEART AND BLOOD-VESSELS 569 

rhage. Expose the brain and the anterior half of 
the spinal cord (page 565). Place the frog on the 
web-board. Note carefully the speed with which 
the corpuscles pass through the smaller vessels 
of the web. The rate of flow in the capillaries is 
the best practical index of the diameter of the 
small arteries. When the arteries constrict, the 
flow in the capillaries will be less rapid. Eemove 
the cerebral hemispheres and the optic lobes. 
After five minutes or more (to allow the frog to 
recover from the shock of the operation), note the 
condition of the web vessels. 

There will be no significant change. 

The removal of the brain anterior to the bulb 
has not destroyed the tonus of the blood-vessels. 

Note the slow rhythmic changes in the diam- 
eter of the vessels. The changes are not uniform 
throughout the length of the blood-vessel. 

2. Curarize the frog sufficiently to paralyze 
the motor nerves. Stimulate the bulb with very 
weak tetanizing currents. 

The flow in the capillaries will be less rapid. 
Obviously the bulb contains nerve cells, the ex- 
citation of which causes the narrowing of the 
blood-vessels. These cells are termed the bulbar 
vasoconstrictor centre. Repeated sections show 
that the vasoconstrictor cells are placed (in the 
rabbit) on both sides of the median line from 



570 THE OUTGO OF ENERGY 

about one millimetre posterior to the corpora 
quadrigemina to a point about four millimetres 
posterior to those bodies. 

The Vasomotor Functions of the Spinal Cord. — 
1. Divide the cord just posterior to the bulb. 
(A fresh frog may be required. In that case, 
remember to curarize.) 

The division of the fibres connecting the vaso- 
constrictor centre with the cord will be followed 
by the dilatation of the vessels in the web (i. e. 
the flow will be more rapid). 

2. Stimulate the peripheral segment of the 
divided cord. 

The blood-vessels will constrict. 

Thus the neuraxons (axis-cylinder processes) 
of the bulbar vasomotor cells pass through the 
spinal cord on the way to their respective blood- 
vessels. 

It should now be determined whether these 
fibres pass to the blood-vessels without interrup- 
tion, or whether they end in contact with spinal 
vasomotor cells through which the connection 
with the blood-vessels is made. 

3. Wait five minutes and then note the flow 
through the capillaries. 

The dilatation observed immediately after the 
separation of the cord from the medulla has given 
place to moderate constriction. The tonus of the 



INNERVATION OF HEART AND BLOOD-VESSELS 571 

blood-vessels has returned. The spinal cord has 
taken up the vasomotor function of the bulb. 
Evidently the spinal cord contains vasomotor 
cells, which ordinarily are subsidiary to those of 
the bulb, but which, when separated from their 
master cells, acquire the power of independent 
action. 

Effect of Destruction of the Spinal Cord on the 
Distribution of the Blood. — Further evidence of 
the vasomotor function of the spinal cord is 
afforded by the following experiment. 

Expose the heart, avoiding unnecessary loss of 
blood. Lay bare the upper part of the intestine 
by an incision on the left side of the umbilical 
vein, which lies in the median line. Suspend the 
frog vertically. Note that the heart and the great 
vessels are filled with blood. Note also the size 
and number of the vessels in the walls of the 
stomach and intestines. 

Bend the frog's head. Put the seeker into the 
vertebral canal and pass it gently downwards to 
destroy the spinal cord. The seeker will move 
easily, if really in the canal. Look at the heart 
and great arteries. 

The heart will soon be bloodless, though beating 
regularly. Examine the vessels of the stomach 
and intestine. They are distended. Evidently, 
the contents of the heart and the great arteries 



572 THE OUTGO OF ENERGY 

have passed into dilated smaller arteries and 
veins. It would be found, on waiting, that this 
effect is not a passing consequence of inhibition. 
The destruction of the spinal cord has changed 
the distribution of the blood. 

The Vasomotor Fibres leave the Cord in the 
Anterior Roots of Spinal Nerves. — 1. Remove 
the arches of the 5th, 6th, 7th, 8th, and 9th ver- 
tebras and lay bare the cord in a large frog in 
which the motor nerves have been paralyzed with 
curare. Note the capillary flow in the web. On 
the side on which the web- vessels are examined, 
tie a silk thread around each of the anterior roots 
near their origin from the cord, and sever the roots 
between the ligature and the cord. 

The vessels will dilate. 

2. Stimulate the peripheral ends of several of 
the divided roots. 

Constriction will follow. 

The vascular dilatation which follows the de- 
struction of the spinal cord is not permanent. 
After a time the vessels regain their tonus. It is 
probable, therefore, that vasomotor nerve cells 
exist outside the spinal cord, and this conclusion 
is confirmed by the results gained on warm-blooded 
animals with the nicotine method. Langley has 
found that the injection of about ten milligrams 
of nicotine into a vein of a cat will prevent, for a 



INNERVATION OF HEART AND BLOOD-VESSELS 573 

time, the passage of nerve impulses through sym- 
pathetic cells. Painting the ganglia with nicotine 
has the same effect. In animals the sympathetic 
cells of which have thus been paralyzed, the stim- 
ulation of the lumbar nerves in the spinal canal 
produces no change in the vessels of the genera- 
tive organs, though in animals not poisoned with 
nicotine this stimulation causes marked constric- 
tion. The lumbar vasomotor fibres must there- 
fore end in connection with sympathetic nerve 
cells which transmit the constrictor impulse to 
the blood-vessel. Similar observations in other 
regions warrant the belief that all the vasomotor 
fibres emerging from the spinal cord end in like 
manner. 

Thus the vasoconstrictor system probably con- 
sists of three neurons. The first is a sympa- 
thetic cell, lying apart from the central nervous 
system. Its neuraxon (axis-cylinder process) 
passes directly to the blood-vessel. The second 
is a spinal cell, the neuraxon of which leaves the 
cord and terminates in contact with the sympa- 
thetic , cell or its branches. The third has its 
cell body in the bulb and its neuraxon termi- 
nates in contact with the second neuron. 

Commonly, as for example in the nerves of the 
extremities, the sympathetic neuraxon passes 
from the ganglion along the gray ramus into the 



574 THE OUTGO OF ENERGY 

corresponding spinal nerve, in which it continues 
to its distribution. 

Vasoconstrictor Fibres in the Sciatic Nerve. — 
Curarize a frog sufficiently to paralyze the volun- 
tary muscles (any excess of curare will paralyze 
the vasomotor fibres also). Carefully destroy the 
brain with the seeker, avoiding loss of blood. 
Expose the right sciatic nerve for a short distance 
on one side, using the greatest care not to injure 
the blood-vessels. Tie a thread tightly around 
the nerve near the upper end of the exposed por- 
tion. Lay the frog, back upward, on the web-board, 
placing the web of the right foot over the notch, 
and securing it with fine pins. Examine the web 
under a low power, to make sure that the circu- 
lation has not been interrupted by stretching the 
web. Place the secondary at such a distance 
from the primary coil that the induced current 
shall be barely perceptible to the tongue. Set 
the hammer vibrating, and close the short-circuit- 
ing key. Put the electrodes under the sciatic 
nerve on the peripheral side of the ligature. Let 
a second observer watch a small vessel of the web 
through the microscope. Open the short-circuit- 
ing key for a moment only. 

The blood-stream slows from constriction of 
the supplying vessels, the contraction increasing 
during a few seconds and then subsiding. 



INNERVATION OF HEART AND BLOOD-VESSELS 575 

This experiment requires much care and close 
observation. The curare effect must be very 
slight; a small quantity of the drug should be 
given an hour before the observation is made. 
Great pains must be taken to use feeble currents 
and not to prolong the excitation, for the vaso- 
motor nerves are rapidly exhausted. The nar- 
rowing of the arteries of the web is usually 
evident only in the slowing of the blood-stream 
during excitation. 

Vasodilator Nerves. — 1. Kepeat the preceding 
experiment in a frog in which the sciatic nerve has 
been four days severed (without injury to the fem- 
oral vessels). On stimulation of the peripheral 
segment of the divided sciatic nerve, the vessels 
of the web will dilate instead of constricting. 

Evidently the sciatic nerve contains vasodilator 
as well as vasoconstrictor fibres. When the 
sciatic fibres are separated from their cells of 
origin by the section of the nerve, the fibres distal 
to the section degenerate. But the degeneration 
does not proceed at the same rate in all the fibres. 
The vasoconstrictors die before the vasodilators. 
In ordinary stimulation of the normal nerve, the 
action of the constrictors overpowers that of the 
dilators. In the partially degenerated nerve, 
the same stimulation causes dilatation because 
the constrictor fibres are dead or dying. 



576 THE OUTGO OF ENERGY 

2. Note the rate of flow in the web-vessels in 
the uninjured limb. Stimulate the sciatic nerve 
with the single induction current repeated at 
intervals of five seconds. 

The vessels of the web will dilate. 

The vasoconstrictor and vasodilator fibres also 
react differently to cold. If the hind limb (cat) 
be cooled, the stimulation that normally causes 
vasoconstriction will cause vasodilatation. 

Vasoconstrictor and vasodilator fibres are not 
always found in the same nerve-trunks ; in the 
chorda tympani nerve, for example, there are only 
dilator fibres. 

The central relations of the dilator nerves have 
not been sufficiently studied to warrant their 
discussion here. 

Reflex Vasomotor Actions. — 1. Note the rate 
of flow in the vessels of the web in a lightly 
curarized frog. Stimulate the skin (not too near 
the bulb or cord) with tetanizing currents. The 
stimulus must not be repeated often, or fatigue 
will obscure the result. 

Keflex constriction of the vessels will take place. 
The sensory impulse is carried by afferent fibres 
to the vasomotor centres. 

Eepeat the experiment, using in place of the 
electrical a mechanical stimulus, such as pinching 
the skin with forceps. 



INNERVATION OF HEART AND BLOOD-VESSELS 577 



Apparatus 

Normal saline. Bowl. Towel. Pipette. Glass plate. 
Inductorium. Key. Wires. Dry cell. Electrodes. 
Needle electrodes. Frog-board. Electromagnetic signal. 
Heart-holder. Kymograph. Glass tube for oesophagus. 
Two muscle levers. Solutions of nicotine (0.2 per cent), 
atropine (0.5 per cent), muscarine (a trace in normal salt 
solution). Curare. Ether. Sponge. Glass jar. Ver- 
tebral saw. Web-board. Fine pins. Microscope. Frog, 
the sciatic nerve of which has been severed four days. 
Millimetre rule. Silk thread. 



37 



INDEX 



Aberration, chromatic, 432, 434 ; diaphragm, 434 ; spherical, 
by reflection, 426 ; spherical, by refraction, 427, 434. 

Absolute force of muscle, 358. 

Accommodation, 469 ; angle between light and visual axis, 
487 ; far point, 479 ; iris, 474 ; lens, 474, 475, 477 ; line, 472; 
measurements, 479 ; mechanism, 473 ; pupil, 473 ; pupil, near- 
ness, 488 ; pupil, size, 488 ; range, 471, 484. 

Acuteness of vision, 465, 466. 

Action current, brain and cord, 319; decrement, 309; dura- 
tion, 314; glands, 320; heart, 310, 312; threshold value, 
318; human muscle, 309; muscle, 300; nerve, 315; optic 
nerve, 318; positive after current, 317; positive variation, 
316; precedes change in form, 311; tetanus, 305; voltage, 
315. 

Afferent impulses, reflex action, 371 ; summation, 372. 

Alteration hypothesis of nerve and muscle current, 299. 

Amalgamation, 46 

Ametropia, determination of, 493. 

Angle, construction of tangent, 467 ; incidence, 403 ; reflection, 
403 ; refraction, 411 ; sine, 414 ; visual, 464. 

Angle gamma, 464. 

Animal heat, 285. 

Ankle jerk, 376. 

Anodes and cathodes, physiological, 110. 

Anterior roots, vasomotor fibres, 572. 

Aortic regurgitation, 550. 

Aortic stenosis, 551. 

Aperture, 420, 427. 

Apparatus, criticism of, 84. 

Arrhenius, theory of dissociation, 31. 

Artificial scheme, 511. 

Astigmatism, 464 ; measurement, 495. 

Atropine, action on heart, 564. 

Augmentor centre, 566. 

Axis, optical, 419 ; optical, eye, 439 ; principal, 419 ; visual 463. 



580 INDEX 

Balancing experiment, 379. 

Bernstein's experiment, 531 ; rheotome, 313. 

Blood pressure, arterial in frog, 522 ; influenced by inhibition, 

525 ; peripheral resistance, 523. 
Blood-vessels, innervation, 568. 
Brain of frog, 565. 
Brain, destruction by pithing, 97 ; dorsal view, 293. 

Calcium, in normal solution, 165. 

Calorimeter, Rubner's experiment, 285. 

Carbon dioxide, action on nerve, 172 ; apparatus, 173. 

Caustic surface, 427-429. 

Cell, dry, 52 : Daniell, 48 ; galvanic, 34. 

Cell, in series, 133. 

Centre, rotation, 463 ; optical, 420 ; optical, crystalline lens, 446. 

Centres of heart nerves, 564. 

Cerebral hemispheres, removal of, 378. 

Chemical stimulation, 163. 

Circle, dispersion, 429, 470-472. 

Circulation, artificial scheme, 511; capillary, 262, 569; inter- 
mittent and continuous, 515 ; mechanics of, 508; mesentery, 
519 ; rate of flow and width of bed, 519. 

Clamp, double, 65 ; flat-jawed, 65 ; Gaskell, 103 ; round-jawed, 
65. 

Clausius, theory of dissociation, 29. 

Closing contraction, 98. 

Color blindness, 501. 

Compensation of demarcation current, 294. 

Compensatory pause, 533. 

Conductivity, 168; centripetal and centrifugal, 181; during 
constant current, 123. 

Contraction, tonic, 141. 

Contraction, direction of current, 157; human muscle, 353; 
idiomuscular, 166; law, 113; load, 341 ; opening and closing, 

I 98 ; rhythms, 142 ; single, 332 ; temperature, 342 ; tonH 107, 
140 ; veratrine, 345 ; wave, 338 ; heart muscle, 534. 

Contracture, 340. 

Coordinated actions, 378. 

Croak reflex, 379. 

Curare, 97 ; poisons end plates, 171. 

Daniell cell, 48. 

Decrement of action current, 309. 

Demarcation current, 287, 295 ; hypotheses, 297 ; interferes 
with stimulating current, 292 ; measurement, 292 ; muscle, 
287 ; negative variation, 305 ; nerve, 296 ; stimulus, 289, 296. 

Dennett's method, numbering prisms, 435. 



INDEX 581 

Depressor nerve, 568. 

Deviation, angular, 435. 

Dicrotic notch, 545. 

Diffusion of gases, 14. 

Dioptre, 435.' 

Dispersion circle, 429, 470, 471, 472. 

Distance, focal, crystalline lens, 450 ; principal focal, cornea, 

441. 
Distilled water, a chemical stimulus, 163. 
Drying, 149, 164. 

DuBois-Reymond, molecular theory, 298. 
Duchenne's points, 127. 
Duration of stimulus, 138. 

Elasticity and extensibility, of a metal spring, 364 ; of a rub- 
ber band, 364 ; of skeletal muscle, 365. 

Electric fish, 329. 

Electrical units, 35. 

Electrodes, for human nerves, 132; indifferent, 111 ; non-polariz- 
able, 93 ; platinum, 65. 

Electrolysis, 26. 

Electrolytic solution pressure, 32. 

Electrometer, 34. 

Electromotive force, 34, 287 ; demarcation current, 292. 

Electrotonic currents, 323 ; as stimulus, 328 ; negative and 
positive variation, 325 ; polarization increment, 325. 

Energy, set free in various forms, 10 ; stimulation, and irrita- 
bility, 7 ; developing, 361. 

Emmetropia, 490; angle of ,' 464. 

Engelmann's incisions, 534. 

Ergograph, 354. 

Excitation wave, 336 ; remains in original fibre, 181. 

Extensibility, 364, 366. 

Extra contraction of heart, 533. 

Eye, artificial, opbthalinoscopie, 489 ; as camera obscura, 437; 
normal measurements, 461 ; see optical box, 404 ; reduced, 
458 ; schematic, 438. 

Extra current in iuductorium, 68. 

Fatigue, 367 ; human muscle, 368 ; polar, 147. 

Fixation, line, 463. 

Focus, conjugate, concave mirror, 427 ; conjugate, convex lens, 

418; conjugate, cornea, 444; principal, concave mirror, 405; 

principal, construction, 443; principal, convex lens, 416; 

principal, eye, 454. 
Focal distance, concave mirror, 406 ; principal, convex lens, 417. 
Focal line, 427. 



582 INDEX 

Food materials, composition of, 281. 

Flexors and extensors, relative excitability, 177. 

Frog board, 112. 

Galvanic cells, electromotive force in, 34. 

Galvanic stimulation may cause periodic impulses, 144. 

Galvanotropism, 137. 

Gas chamber, 173. 

Gaskell's block, 535 ; clamp, 103. 

Goltz's experiment, 567. 

Gower's experiment, 376. 

Graphic method, 77. 

Heart, action current, 310, 312 ; apex, isolated, 531 ; atropine, 
564 ; augmentor centre, 566 ; augmentor nerves, 555 ; auric- 
ulo- ventricular interval, 561 ; Bernstein's experiment, 531 ; 
calcium, 539 ; change in form, 529 ; chemical theory, 540 ; 
compensatory pause, 533 ; constant stimulus, 532 ; contrac- 
tion curve, 530 ; contraction wave, 534 ; excitation from auri- 
cle to ventricle, 535; exposure, 112; extra contraction, 
533 ; Gaskell's block, 535 ; graphic record, 530 ; impulse, 
541 ; inhibited, 559 ; inhibitory centre, 564 ; inhibitory mech- 
anism, 562 ; inorganic salts, 538 ; irregularities, 536 ; irritable 
though inactive, 533; irritable though inhibited, 561 ; load, 
537 ; maximal contraction, 530; monopolar stimulation, 111 ; 
muscarine, 564; nerve-free, 170; nicotine, 563; outflow 
period, 526; polar inhibition, 153; polar stimulation, 110; 
potassium, 539; pump, 525; reflex augmentation, 568; re- 
flex inhibition, 567 ; refractory period, 533 ; rhythmic con- 
tractility, 532 ; sounds, 541 ; staircase contraction, 531 ; tonus, 
537 ; Stannius inhibition, 562 ; sympathetic, 556 ; tempera- 
ture, 538; vagus, 559; valves, 511, 525, 550, 551, 552. 

Heat values, calculation, 285. 

Htpermetropia, 431 ; angle of, 464 ; measurement, 495. 

Idio-muscular contraction, 166. 

Image, concave mirror, 405, 409-; convex mirror, 410 ; convex 
lens, 419, 420 ; cornea, 443 ; dioptric, 456, 457 ; retinal, 437 ; 
retinal, actual size, 465 ; retinal, apparent size, 464 ; smallest 
perceptible, 466 ; virtual, concave mirror, 408 ; virtual, con- 
cave lens, 419. 

Index of refraction, 412. 

Induction currents, 54 ; direction, 158 ; gap in resulting contrac- 
tions, 161; magnetic, 56, 58; nerves, 69 ; stimulus, 66, 158; 
unipolar, 71. 

Inductorium, 54; construction, 60; graduation, 83. 



INDEX 583 

Inhibition, galvanic, 153; heart, 559; polar, 155; reflex of 
heart, 567 ; ventricular, 524. 

Inhibitory nerves of heart, 558. 

Inhibitory centre, 564. 

Interrupter, 62, 303. 

Ions, 28. 

Iris, accommodation, 474. 

Irritability, 169 ; definition, 9 ; different points of same nerve, 
180 ; flexor and extensor nerves, 177 ; muscle, independent, 
169 ; nerve greater than muscle, 179 ; separable from conduc- 
tivity, 172. 

Isometric contraction, 352, 355 ; method, 349. 

Isotonic method, 349. 

Isotony, 20. 

Key, short-circuiting, 46 ; simple, 45 ; rocking, 50. 

Kinetic theory, 12. 

Knee jerk, 375. 

Kymograph, 79; long paper, 81. 

Lantern, 404. 

Latent period of muscle, 334. 

Lens, accommodation, 474, 475; concave, 422; convex, 416; 

numbering, 435. 
Lever, light muscle, 86 ; heavy or rigid, 351 ; writing, 87. 
Light, spectrum, 413. 

Line of fixation, 463 ; focal, 427 ; force, 57. 
Load, influence on contraction, 537. 

Magnetic field, 57 ; induction, 57. 

Make or break current excluded, 70; stimuli, 67. 

Manometer, mercury, 523. 

Mechanical stimulation, 166. 

Mirror, concave, 405 ; convex, 410 ; plane, 403. 

Mitral incompetence, 552. 

Moist chamber, 95. 

Molecular hypothesis of nerve and muscle current, 298. 

Monopolar stimulation, 111. 

Motor points, 128. 

Muscarine, action on heart, 564. 

Muscle, action current, 300 ; clamp, 8 ; curve, 333 ; demarca- 
tion current, 287 ; form affects stimulation, 156 ; left hind 
limb of frog, 6, 99; lever, 86, 351; tonus, 389; turbid and 
clear, 335 ; warmer, 343. 

Myomeres, 298. 

Myopia, 430 ; angle of, 464 ; measurement, 493. 



584 INDEX 

Negative variation, 321 ; electrotonic currents, 325 ; secretion 
currents, 321. 

Nerve, action current, 315 ; cervical in frog, 558 ; conducts in 
both directions, 181; conductivity, 120; conductivity and 
irritability, 172; demarcation current, 295; drying, 149 
electrical resistance, 327 ; electromotive phenomena, 295 
impulse, speed of, 184 ; induction, 69 ; inhibitory, 558 
irritability, 116; irritability compared with muscle, 179 
irritability, different points, 180 ; irritability, specific, 179 
polarization, 323 ; polar stimulation, 113, 131 ; stimulated by 
own demarcation current, 296. 

Nerve-muscle preparation, 4. 

Nicotine, action on heart, 563. 

Nitrite of amyl, 550. 

Normal saline solution, 165. 

Ophthalmoscope, 489. 

Ophthalmoscopy, 484 ; direct, 490 ; indirect, 496. 
Optic nerve, action current, 318. 
Optical box, 404. 

Opening and closing contraction, 98, 125 ; tetanus, 147. 
Ordinates, 91. 
Osmometer, 18. 

Osmotic pressure, 16; blood-corpuscle method, 22; blood 
serum, 21. 

Paper, smoked, method of using, 78. 

Paradoxical contraction, 328. 

Paramecium, galvanotropism, 137. 

Partial pressure, 13. 

Periodic contraction from chemical stimulation, 165; galvanic 
stimulation, 144. 

Peripheral resistance, 521. 

Permeability, 24. 

Pithing, 97: 

Plasmolysis, 20? 

Plethysmograph, 545. 

Point, cardinal, cornea, 440 ; cardinal, crystalline lens, 445 ; 
cardinal, eye, 439, 451 ; far, accommodation, 479 ; far, deter- 
mination, 479 ; near, accommodation, 480 ; near, determina- 
tion, 480; nodal, 420; nodal, crystalline lens, 447; nodal, 
eye, 453 ; principal, crystalline lens, 450 ; s, 449, 453. 

Polar excitation, 148; fatigue, 147; inhibition, 153, 155; in- 
jured muscle, 151 ; refusal, 292; stimulation, 101, 113, 159. 

Polarization, 46 ; current, 51, 145 ; increment, 325 ; positive 
variation, 146. 

Pole-changer, 49, 50. 



INDEX 585 

Positive after current, 317. 

Positive variation, action current, 316 ; polarization current, 
146 ; polarizing current, 325. 

Prentice's method, numbering prisms, 435. 

Prisms, 413 ; construction, 413 ; numbering, 435 ; path of en- 
tering ray, 413. 

Pulse, aortic regurgitation, 550; curve, 546; dicrotic, 545; 
form, 544 ; frequency, 543 ; hardness, 544 ; low tension, 549 ; 
pressure, 545; valvular disorders, 551, 552; volume, 545, 
552. 

Pupil, accommodation, 473. 

Reaction of degeneration, 135. 

Reaction time, 382. 

Reflection, concave mirror, 405; convex mirror, 410; plane 
mirror, 403. 

Reflex actions, 370; afferent impulses, 371 ; cornea, 374 ; inhi- 
bition, 384 ; man, 374 ; pupil, 375 ; purpose, 381 ; segmen- 
tal, 373 ; strychnine, 377 ; tendon, 375 ; threshold, 372 ; 
throat, 382 ; vasomotor, 576. 

Reflex time, 382. 

Refraction, 410; concave lens, 422 ; convex lens, 416; convex 
and cylindrical lenses, combined, 424 ; cylinders, 422 ; eye, 
437; index, 412; prism, 413. 

Refractory period, 534. 

Respiration, mechanics of, 505. 

Respiration scheme, 505. 

Retina, reflection, 484. 

Rheochord, 42. 

Rheoscopic frog, 302, 306. 

Rheotachygraph, Hermann, 314. 

Rheotome, differential, Bernstein, 313. 

Ringer solution, 540. 

Ritter-Rollett phenomenon, 177. 

Salts, influence on contraction of hearty 538. 

Saturation, 16. 

Scheiner's experiment, 469. 

Sciatic nerve, vasomotor fibres, 574. 

Secretion current, 320; negative variation, 321. 

Semi-permeable membrane, 17. 

Shortening in single contraction and in tetanus, 348. 

Sensation, effort. 400; general, 398 ; irradiation, 398; motion, 
400 ; motor, 400 ; pain, 399 ; pressure, 393 ; taste, 401 ; tem- 
perature, 390 ; tickle, 398; touch, 395 ; Weber's law, 395. 

Signal, electro-magnet, 105. 

Size, apparent, 456, 465. 



586 INDEX 

Skin, hot and cold spots, 390 ; irradiation, 398; pressure spots, 
393. 

Smooth muscle, 356. 

Solution, gas in liquid, 16; normal, 165; solid in liquid, 16; 
tension, 16. 

Spectrum, 413, 432. 

Sphygmograph, 527. 

Spinal cord, localization of movements at different levels, 387 ; 
destruction changes distribution of blood, 571. 

Spinal nerve roots, 386 ; sensory nerves, 388. 

Spontaneous contractions, 356. 

Staircase contraction, beart, 531. 

Stannius ligature, 562. 

Stimulation, 9; angle of current lines, 157; chemical, 163, 164; 
constant, may cause periodic contraction, 165 ; demarcation 
current, 290, 296; distilled water, 163; drying, 164; form 
of muscle, 10, 156; induction current, 158; intensity changes, 
99; mechanical, 166; minimal and maximal, 175; monopo- 
lar, 111; polar, in heart, 110; summation of impulses, 176; 
threshold value, 1 74 ; unipolar, errors, 320. 

Stroboscopic method, 305. 

Surface, caustic, 427, 428, 429 ; principal, crystalline lens, 
418 ; principal, eye, 449. 

Surface tension, 25, 36. 

Summation of stimuli, 176. 

Superposition in tetanus, 347. 

Superposition of two contractions, 346. 

Sympathetic, action on heart, 556 ; frog, 556 ; preparation, 
555. 

Synchronous poiuts, method of obtaining, 120. 

System A, schematic eye, 440 ; B, schematic eye, 445 ; C, 
schematic eye, 451. 

Temperature, hourly variation, 285 ; mouth, affected by food, 
285; reaction to variations in, 285 ; regional, 285. 

Tension indicator, 25. 

Tetanus, 69, 346 ; electrical phenomena, 305 ; natural and arti- 
ficial, 355 ; opening and closing, 147 ; Ritter's, 149. 

Threshold value of stimulation, 175. 

Tonus of heart muscle, 537. 

Tradescantia discolor, 20. 

Tuning fork, 88. 

Unipolar induction, 71, stimulation, errors, 320. 

Van der Waal's hypothesis, 14. 
Van't Hoff's discoveries, 20. 



INDEX 587 

Vagus, preparation, 558; inhibits heart-beat, etc., 559, 560, 

561. 
Vapor pressure, 15. 
Vasodilator nerves, 575. 
Vasomotor centre, 570 ; fibres in anterior roots, 572 ; functions 

of cord, 570 ; reflexes, 576 ; sciatic, 574. 
Veratrine, influence on contraction, 345. 
Vision, acuteness, 465, 466 ; blind spot, 499 ; color blindness, 

501 ; field of, 500 ; yellow spot, 499. 
Volume of contracting muscle, 331. 
Volume tube, 332. 

Wohler's discovery, 3. 

Work adder, 359. 

Work done, influenced by load, 358. 



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